Muscular-skeletal tracking system and method

ABSTRACT

At least one embodiment is directed to a tracking system for the muscular-skeletal system. The tracking system can identify position and orientation. The tracking system can be attached to a device or integrated into a device. In one embodiment, the tracking system couples to a handheld tool. The handheld tool with the tracking system and one or more sensors can be used to generate tracking data of the tool location and trajectory while measuring parameters of the muscular-skeletal system at an identified location. The tracking system can be used in conjunction with a second tool to guide the second tool to the identified location of the first tool. The tracking system can guide the second tool along the same trajectory as the first tool. For example, the second tool can be used to install a prosthetic component at a predetermined location and a predetermined orientation. The tracking system can track hand movements of a surgeon holding the handheld tool within 1 millimeter over a path less than 5 meters.

FIELD OF THE INVENTION

The invention relates in general to medical and surgical procedures andmore particularly to guiding medical devices to precise locations on orwithin a patient's body.

BACKGROUND OF THE INVENTION

Precisely positioning inserts, implants, or other medical devices,prostheses, prosthetic components, or topical application of medicinesor anesthetics in or on patients' bodies depends on accurately locatingstructural features or anomalous structures on or within a patient'sbody. Continual progress has been made in the advancement and use ofimaging equipment to guide the positioning of inserts, implants, orother medical devices, within patients' bodies. Noninvasive methods forlocating internal structures of the body include ultrasound, X-rays, CT,and MRI equipment to locate anatomical features and anomalous structureswithin patients' bodies. Surgeons may use this data to create apre-operative template to guide actions during the surgery.

The use of pre-operative images to guide the precise placement andorientation of medical devices or prosthetic components during surgerymay require real-time scanning of patients' bodies or the use ofrobotics. Much of this requires large and expensive equipment.Alternatively, physical observation by the physician or surgeon, aidedby the pre-operative scans and template, may guide placement of inserts,implants, or other medical devices, or prostheses or prostheticcomponents within patients' bodies.

Trialing is also critical in many implant procedures. The use of trialdevices or prosthetic components provides a useful guide to theselection of the prosthetic components to be included in the chronicprosthetic implant as well as confirmation of the fit and functioning ofthe selected prosthetic components in vivo.

Even with templating, trialing, and advanced prosthetic components,outcomes including functional efficacy, patient comfort, and longevityof the prosthesis may not always be highly predictable, especially ifprocedures are performed by physicians and surgeons with differentlevels of skill, experience, and frequency of repeating an individualprocedure. This may be confirmed by various reports in the literaturethat suggest a positive relationship between outcomes and the numbers ofprocedures performed annually by individual surgeons.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of present invention will become more fully understood fromthe detailed description and the accompanying drawings, wherein:

FIG. 1 illustrates a simplified view of a physician using at least oneembodiment of a motion and orientation sensing device (e.g., a surgicaltracking system) with a computer display (e.g., a surgical trackingdisplay system);

FIG. 2 illustrates a simplified view of a physician holding aninstrument having an embodiment of a motion and orientation sensingdevice with a computer display of the instrument's location andorientation approaching a pre-specified target;

FIG. 3 illustrates a simplified view of a physician holding aninstrument having an embodiment of a motion and orientation sensingdevice with a computer display defining the instrument's location andorientation at some distance from a pre-specified target plus a secondmotion and orientation sensing device pinned to a patient to track anymovement of the target;

FIG. 4 illustrates a simplified view of a physician holding aninstrument having an embodiment of a motion and orientation sensingdevice with a computer display defining the instrument's location andorientation approaching a pre-specified target while a second motion andorientation sensing device pinned to a patient tracks any movement ofthe target;

FIG. 5 illustrates a simplified perspective view of an example of amotion and orientation sensing device, a cover for the device;

FIG. 6A illustrates a simplified perspective view of an example of aninstrument (e.g., surgical device holder) having an example motion andorientation sensing device (e.g., tracking element), a cover for thedevice, an interchangeable head, and an example insert or implant (e.g.,surgical device) that may be held by the instrument (e.g., surgicaldevice holder);

FIG. 6B illustrates a simplified perspective view of an assembledexample of an instrument having an example motion and orientationsensing device, a cover for the device, an interchangeable head, and anexample insert or implant held by the instrument;

FIG. 7 illustrates a simplified example of a top-level flow chart of thesteps performed by an example system having an embodiment of the motionand orientation sensing module or device and a computer system forguiding an instrument to return to its initial position;

FIG. 8 illustrates a simplified example of a flow chart of the stepsperformed by a physician or other user preparing to use an exampleembodiment of the motion and orientation sensing module to guide aninstrument to return to its initial location and orientation;

FIG. 9 illustrates a simplified example of a flow chart of the stepsperformed by an example embodiment of the motion and orientation sensingmodule to prepare for tracking of changes in its location andorientation;

FIG. 10 illustrates a simplified example of a flow chart of the stepsperformed by a computer to capture the initial orientation data from anexample embodiment of the motion and orientation sensing module ordevice;

FIG. 11 illustrates a simplified example of a flow chart of the stepsperformed by a computer to capture the distance and direction of theinitial movement of an example embodiment of the motion and orientationsensing module or device;

FIG. 12 illustrates a simplified example of a flow chart of the stepsperformed by a computer to capture the initial 100 movements of anexample embodiment of the motion and orientation sensing module ordevice;

FIG. 13 illustrates a simplified example of a flow chart of the stepsperformed by a computer to analyze and display the initial 100 movementsand changes in orientation of an example embodiment of the motion andorientation sensing module or device;

FIG. 14 illustrates a simplified example of a flow chart of the stepsperformed by a computer to analyze each additional movement and changein orientation of an example embodiment of the motion and orientationsensing module or device;

FIG. 15 illustrates a simplified example of a flow chart of the stepsperformed by a computer to display each additional movement and changein orientation of an example embodiment of the motion and orientationsensing module or device;

FIG. 16 illustrates a simplified example of a flow chart of the stepsperformed by a computer to process exception conditions andautomatically trigger the shutdown procedure if that becomes necessaryto protect the integrity of the tracking procedure while maintainingdata integrity;

FIG. 17 illustrates a simplified example of an initial computer displayscreen that can be used to guide the movement and orientation of aninstrument having an example embodiment of a motion and orientationsensing module or device;

FIG. 18 illustrates a simplified example of a computer display screenillustrating the position and location of an instrument having anexample embodiment of a motion and orientation sensing module or deviceas it is starting to approach the pre-defined target location andorientation;

FIG. 19 illustrates a simplified example of a computer display screenillustrating changes in the display as an instrument having an exampleembodiment of a motion and orientation sensing module or device is movedtowards the target location and orientation;

FIG. 20 illustrates a simplified example of a computer display screenillustrating changes in the display as an instrument having an exampleembodiment of a motion and orientation sensing module or deviceapproaches the target location and orientation;

FIG. 21 illustrates a simplified example of a computer display screenillustrating the final position and orientation of an instrument havingan example embodiment of a motion and orientation sensing module ordevice precisely aligned with the target location and orientation;

FIG. 22 illustrates a simplified perspective of a cut-away view of anexample motion and orientation sensing module or device;

FIG. 23 illustrates a simplified block diagram of an example informationtechnology system and components integrating the data captured by amotion and orientation sensing module or device and displaying itsprogress in real time;

FIG. 24 illustrates a simplified block diagram of the basic constructionof a generic accelerometer at rest;

FIG. 25 illustrates a simplified block diagram of the basic constructionof a generic accelerometer under acceleration;

FIG. 26 illustrates a simplified block diagram of the orientation ofgeneric accelerometers within a tri-axial accelerometer;

FIG. 27 illustrates a simplified schematic block diagram of an examplemotion and orientation sensing module or device having tri-axialcapacitive accelerometers;

FIG. 28 illustrates a simplified schematic block diagram of an examplemotion and orientation sensing module or device having tri-axialpiezoresistive accelerometers;

FIG. 29 illustrates a simplified schematic block diagram of an examplemotion and orientation sensing module or device having tri-axialforce-balanced capacitive accelerometers;

FIG. 30 illustrates a simplified schematic block diagram of a basicgeneric accelerometer embodiment integrated with filtering, dithering,oversampling, and decimation functions to improve the signal to noiseration and the effective number of bits;

FIG. 31 illustrates a simplified schematic block diagram of an examplemotion and orientation sensing module or device having tri-axialforce-balanced capacitive accelerometers incorporating filtering,dithering, oversampling, decimation, ratiometric, and temperaturesensing functions to improve the signal to noise ration and theeffective number of bits; and

FIG. 32 illustrates a simplified schematic block diagram of an examplemotion and orientation sensing module or device having tri-axialpiezoresistive accelerometers incorporating filtering, dithering,oversampling, decimation, ratiometric, temperature sensing, and eventdetection functions to improve the effective number of bits andrepeatability of data collection and processing.

DETAILED DESCRIPTION OF EMBODIMENTS

The following description of embodiment(s) is merely illustrative innature and is in no way intended to limit the invention, itsapplication, or uses.

At least one embodiment is directed to a portable or handheld, wired orwireless dual tri-axial accelerometer device that facilitatesreplacement of a surgical instrument to a desired location, such anembodiment enables a cost effective alternative for performing manymedical and surgical procedures. At least one embodiment is directed toa surgical tracking system that emits no harmful radiation, is lightweight, requires minimal training, is inexpensive, flexible enough tosupport multiple procedures, can track real time motion of surgicaldevices and patients, and can include other biometric data sets.

Utilizing an accelerometer or other methods of the embodiments forsurgical instrument placement reduces the invasiveness of many medicaland surgical procedures without compromising the precision of locatingprobes, instruments, instruments, inserts, implants, and other medicaldevices with respect to anomalous structures on or within patients'bodies, boney landmarks within patients' bodies, structural features onor within patients' bodies, or centers of rotation within patients'joints. Data gathered from the location devices in embodiments can bereadily integrated into electronic health record systems and databasesto facilitate sharing of patients' medical data among appropriatephysicians and surgeons. Reducing invasiveness, as well as improvingaccess to medical records data, improves patient safety and reducesoverall healthcare costs to the patient, as well as to society.

At least one embodiment is directed to guiding probes, instruments, orsimilar apparatus to precise locations on or within a patient's body, aswell as precisely positioning inserts, implants, or other medicaldevices, or topical application of medicines or anesthetics in or onpatients' bodies.

Utilizing an accelerometer or other methods of the embodiments forsurgical instrument placement enables highly effective trialingprocedures with the placement and orientation of chronic prostheticcomponents precisely duplicating the position and orientation of trialcomponents or devices. Therefore the intra-operative resultsdemonstrated with the trial component are accurate predictors of theperformance of the chronic prosthetic implant.

At least one embodiment is directed to a portable, handheld device foraccurately guiding probes, instruments, instruments, to preciselocations on or within a patient's body, as well as preciselypositioning inserts, implants, other medical devices, or prostheses orprosthetic components within patients' bodies, or topical applicationsof medicines or anesthetics in or on patients' bodies. Highly preciseand repeatable positioning of medical instruments and devices as well astopical medicines, can improve the efficacy of medical and surgicalprocedures, improve patient comfort and safety, and reduce overallhealthcare costs to the patient and to society.

Herein the surgical tracking system is also referred to as a motion andorientation sensing device.

For simplicity and clarity of the illustration(s), elements in thefigures are not necessarily to scale, are only schematic and arenon-limiting, and the same reference numbers in different figures denotethe same elements, unless stated otherwise. Additionally, descriptionsand details of well-known steps and elements are omitted for simplicityof the description. Notice that once an item is defined in one figure,it may not be discussed or further defined in the following figures.

It will be appreciated by those skilled in the art that the words“during”, “while”, and “when” as used herein relating to circuitoperation are not exact terms that mean an action takes place instantlyupon an initiating action but that there may be some small butreasonable delay, such as a propagation delay, between the reaction thatis initiated by the initial action. Additionally, the term “while” meansthat a certain action occurs at least within some portion of duration ofthe initiating action. The use of the word “approximately” or“substantially” means that a value of an element has a parameter that isexpected to be close to a stated value or position. However, as is wellknown in the art there are always minor variances that prevent thevalues or positions from being exactly as stated.

The terms “first”, “second”, “third” and the like in the Claims or/andin the Detailed Description are used for distinguishing between similarelements and not necessarily for describing a sequence, eithertemporally, spatially, in ranking or in any other manner. It is to beunderstood that the terms so used are interchangeable under appropriatecircumstances and that the embodiments described herein are capable ofoperation in other sequences than described or illustrated herein.

Processes, techniques, apparatus, and materials as known by one ofordinary skill in the art may not be discussed in detail but areintended to be part of the enabling description where appropriate. Forexample specific methods of attaching a surgical device onto thesurgical device holder, however one of ordinary skill would be able,without undo experimentation, to establish the steps using the enablingdisclosure herein.

At least one embodiment is directed to a portable or handheld, wired orwireless device that enables a cost effective alternative for guidingthe positioning of inserts, implants, or other medical devices,prosthetic components, or topical application of medicines oranesthetics in or on patients' bodies. With the aid of embodiments thesemedical and surgical procedures and can be expected to obtain highlyreproducible results. At least one embodiment reduces invasiveness ofmany medical and surgical procedures without compromising the precisionof locating probes, instruments, instruments, inserts, implants,prostheses or prosthetic components and other medical devices withrespect to anomalous structures on or within patients' bodies,structural features on or within patients' bodies, or boney landmarks.Data gathered during a medical procedure are readily integrated intoelectronic health record systems and databases facilitating the sharingof patients' test results among appropriate physicians and surgeons.Reducing invasiveness, as well as improving access to medical recordsdata, improves patient safety and comfort as well as reduces overallhealthcare costs to the individual and to society.

The terms precision and resolution can be used herein to specificallyhave the standard definitions. Precision will connate the variation fromexactness. Resolution will have the customary definition of the smallestmeasurable interval. The orientation of the x, y, z axes of rectangularCartesian coordinates is assumed to be such that the x and y axes definea plane at a given location, and the z axis is normal to the x-y plane.The axes of rotations about the Cartesian axes of the device are definedas yaw, pitch and roll. With the orientation of the Cartesiancoordinates defined in this paragraph, the yaw axis of rotation is the zaxis through body of the device. Pitch changes the orientation of alongitudinal axis of the device. Roll is rotation about the longitudinalaxis of the device.

The orientation of the x, y, z axes of rectangular Cartesian coordinatesis selected to facilitate graphical display on computer screens havingthe orientation that the user will be able to relate to most easily.Therefore the image of the device moves upward on the computer displaywhenever the device itself moves upward for example away from thesurface of the earth. The same applies to movements to the left orright.

The terms ‘motion sensing’ and ‘tilt sensing’ and ‘orientation’ are alsointended to have specific meaning. ‘Motion sensing’ indicates thedetection of movement of a body that exceeds a specified threshold inone or more coordinate axes, for example the specific threshold in oneor more Cartesian axes in terms of both static and dynamic acceleration.‘Heading’ is defined as the orientation of longitudinal axis of themotion of the motion and orientation sensing module or device andmovement in a direction. ‘Tilt’ is defined as the orientation of a bodywith respect to a zenith. Tilt sensing′ indicates the measurement ofacceleration attributable to gravity in one or more axes. ‘Orientation’includes yaw as well as ‘tilt.’ Yaw is not readily quantified byaccelerometers whenever the center of rotation coincides with the centerof the proof mass within an accelerometer. Detection of this rotationmay require two or more accelerometers to assure that at least oneaccelerometer is moved enough to reliably sense motion that accompaniesyaw. Note that although accelerometers are provided as enabling examplesn the description of embodiments, any tracking device (e.g., a GPS chip,acoustical ranging, magnetometer, gyroscope) can be used within thescope of the embodiments described.

At least one embodiment is directed to surgical tracking system whichcan include a motion and orientation sensing module (e.g. trackingelement) or device that can be embedded in, affixed on, or attached tosurgical device holder (e.g., a probe, tool, instrument, alignment jigsor cutting blocks, or similar apparatus) and used to accurately guidesurgical devices (e.g., medical instruments and equipment) to aspecified location and orientation in space with high precision. It canalso be used to guide positioning of other surgical devices such asinserts, implants, or other medical devices, prostheses or prostheticcomponents, or even topical application of medicines or anesthetics inor on patients' bodies. A hermetic, wireless motion and orientationsensing device, having one or more accelerometers, signal processing,telemetry, and control circuitry, nonvolatile memory, and energystorage, harvesting, or receiving components within an enclosure, shell,or body having one or more switches or touch sensitive surfaces, can beused during these medical or surgical procedures. The target locationand orientation can be defined by a previous or initial location andorientation of a probe, instrument, or instrument having a motion andorientation sensing device, or by data from imaging systems orpositioning guides, or by manual or robotic examination andidentification of anatomical structures or landmarks, anomalousstructures on or within the body, by extrapolation or interpolation fromthose landmarks, or anomalous structures on or within a patient's body.This can include surface contact or transcutaneous penetration by aprobe, instrument, or instrument having a motion and orientation sensingdevice attached, affixed, embedded, or integrated at a fixed positionwith respect to its leading edge or active face.

The movement of a probe, tool, instrument, or alignment jigs or cuttingblocks, or similar apparatus having a motion and orientation sensingmodule or device integrated or attached to, embedded into, affixed onto,or integrated within to it can be locally or remotely controlled toaccurately orient and position the tip of the active portion of thecontrolled equipment at the specified point or target in space with highprecision. For example within 1 mm and 1 degree for a path length of 5 mor less. This can facilitate the performance of medical or surgicalprocedures with high levels of consistency and repeatability, as well ascapturing position-related data in real time for preservation inelectronic health records.

Other functions and sensing capabilities can be readily integrated intoa motion and orientation sensing module or device to augment itsfunctional and sensing capabilities and provide additional real-timedata for positioning and orienting probes, instruments, instruments,equipment, and medical devices, implants, prostheses or prostheticcomponents, as well as gathering other forms of pertinent additionaldata. Additional data acquisition capabilities can include sensingpressure, force, temperature, detection of many forms of radiationincluding electromagnetic, electric, or magnetic fields, light, andinfrared, as well as sensing sound and ultrasound. Additional sensingcapabilities and data captured in real time can augment electronichealth records, as well as be useful in supporting refinement of theconsistency and repeatability of medical and surgical procedures. Forexample an additional tracking data set (e.g., position, velocity,acceleration) of the surgical device holder can be acquired from systems(e.g., acoustical ranging, infrared pattern disruption, laserreflection) that can be fed into the surgical tracking display systemand used to improve the position and orientation of the surgical deviceholder.

Accelerometer technology is used in many applications, although few mayhave higher accuracy and precision requirements than highly exactingmedical procedures such as biopsies, orthopedic surgeries, or comparableprocedures require. Few applications have greater reliability and safetyrequirements than medical applications. In fact, some electroniccomponent manufacturers include disclaimers that their products are notqualified for medical applications.

Accelerometers are effective sensors for acceleration as well as tiltwith respect to the center of the earth. In at least one embodiment awireless motion and orientation sensing module or device, having anaccelerometer or accelerometers in addition to other electroniccomponents and electrical circuitry, is used to detect, track, quantize,and transmit motion and changes in orientation in real time. Data can begraphically displayed in real time to aid in guiding movement withrespect to a target location and orientation.

Acceleration is the second derivative of distance traveled. Thereforethe acceleration data can be integrated to estimate velocity andvelocity can be integrated to estimate distance traveled. Theseoperations are readily accomplished with software. Distance traveled, inall three dimensions, can be tracked from a known starting point. Witheach incremental movement of a probe, tool, instrument, alignment jigsor cutting blocks, similar apparatus, or a physician's or caregiver'shand, or robotic arm and gripper, the output of these calculations canbe used to estimate the remaining distance to the target. This distancecan be displayed in real time on a computer driven video display screen.This feedback loop can be used to accurately guide the probe, tool,instrument, alignment jigs or cutting blocks, or probes, instruments,instruments, or similar apparatus held in a physician's or caregiver'shand, or implants, prostheses or prosthetic components, to the targetwith high level of precision, including subcutaneous targets thephysician or caregiver may not be able to view directly.

Error propagates with increased positional and angular derivations. Forexample when obtaining the positional value from a measuredacceleration, the error of the acceleration must be combined with theerror in the time, and the error of the derived initial velocity, whichresults in a larger error in the position than in the acceleration. Onemethod of mitigating propagating errors is to measure position,velocity, and orientation directly and combine the data with theirassociated errors into an algorithm (e.g., Kalman Filter) combining thedata to provide enhanced tracking of the surgical device holder. Forexample current inertial navigation system (INS) chips (e.g., VN-100™)can provide accuracies to <2 degrees of heading with a resolution of<0.05 degrees; a pitch and roll accuracy to <0.5 degrees at a resolutionto <0.05 degrees; an angular rate bias stability (for heading, pitch,roll) to <+/−0.06 degree/sec; and an acceleration bias stability to <3mg (milli-acceleration of gravities). Current INS chips employ the useof microcircuit accelerometers, angular rate gyros and magnetometers asinput to algorithms (e.g. Kalman Filtering) to enhance the accuracy ofthe provided position and orientation data. Note also that the use ofmultiple accelerometers provides an over determined system of equationsthat can be used to improve the position and orientation determination.

Orientation of the tip of the probe, tool, instrument, or alignment jigsor cutting blocks, or similar apparatus, or implants, prostheses orprosthetic components can be as critical as their location. Datadefining the tilt with respect to gravity is also available fromaccelerometers. This data (e.g., tracking data) can be incorporated intothe real-time display (e.g., in a surgical tracking display system) toillustrate the orientation of the surgical device (e.g., probe, tool,instrument, alignment jigs or cutting blocks, or similar apparatus, orprobes, instruments, instruments or similar apparatuses) held in aphysician's or caregiver's hand, or used to automatically guide arobotic arm and gripper, in all three axes simultaneously. This feedbackloop can be used to guide the orientation of the probe, tool,instrument, alignment jigs or cutting blocks, or implants, prostheses orprosthetic components to the target. This can also include subcutaneoustargets the physician or caregiver may not be able to view directly.

The third vector of orientation is the yaw, or heading, of the probe,tool, instrument, or similar apparatus. The motion and orientationsensing module or device having two tri-axial accelerometers quantifiesthe yaw of an associated probe, tool, instrument, or similar apparatus.Yaw is measured and tracked by collecting acceleration data from anaccelerometer positioned at each end of the longitudinal axis of theenclosure of the motion and orientation sensing module or device. Theforward tri-axial accelerometer defines the tilt of the probe, tool,instrument, or similar apparatus with respect to the horizon. Thealgebraic sum of the acceleration in all of the three Cartesian axes ofthe forward tri-axial accelerometer determines the distance between theleading edge, or active face, of the probe, tool, instrument, or similarapparatus and the target. The algebraic sum of the acceleration of thetri-axial accelerometer positioned at the trailing edge of the motionand orientation sensing module or device determines the position of therear of the probe, tool, instrument, or similar apparatus with respectto the distal tip of the probe, tool, instrument, or similar apparatus.From this information the yaw of the probe, tool, instrument, or similarapparatus is calculated. Note that additional embodiments are notlimited to determining the position of the rear of the probe, otherlocations on the probe can be determined. The combination of locationand orientation data calculated from acceleration and tilt data producedby the two tri-axial accelerometers enables a user of the motion andorientation sensing module or device to accurately locate and orient aprobe, tool, instrument, or similar apparatus precisely at its targetlocation and orientation with no discrepancies in pitch, roll, or yaw.

For example, one can sample the dynamic and static acceleration readingsfrom each accelerometer within both triaxial accelerometer ICs with aconstant sample rate. These values can then be captured and recorded inan array of acceleration values. A rectangular approximation of theintegral of the acceleration can be used to compute the average velocityof each sample period. Additional approaches can also used, for examplea 3rd or 4th order approximation method. The direction of accelerationalong one or more axes can reverse during some sample periods, thus theuse of algebraic differences in acceleration during each sample period.Once the algebraic average of the velocity during each period isestimated, a rectangular approximation of the integral of the average ofvelocity can be used to estimate the change in location of the device.These changes in location are algebraically summed as well and when thenet change in location is zero within estimated error, the device hasreturned to its initial location. When both triaxial accelerometers havereturned to their initial locations, the heading of the devicecorresponds to its initial orientation. Whenever the algebraic sum ofthe changes in tilt of the two triaxial accelerometers in the X-Z andY-Z planes is zero the orientation of the device in those two planes hasreturned to their initial values as well.

At least one embodiment uses multiple accelerometers, and a non-limitingexample using two accelerometers can be discussed. Motion andorientation sensing modules and devices having two accelerometers arenot only capable of providing more accurate yaw data, but also twoaccelerometers provide a level of redundancy that aids in theconfirmation that the instrument is guided accurately to the targetposition and orientation. If this cannot be achieved to the requiredlevel of precision for both accelerometers the tracking procedure mayhave been compromised and the user can be alerted to the possibility ofan exception condition that needs to be addressed.

The precision of the final placement and orientation of the probe, tool,instrument, alignment jigs or cutting blocks, or similar apparatus, aswell as implants, prostheses or prosthetic components, depends on threekey factors: the precision of the location and orientation of thestarting point; the accuracy and resolution of the acceleration dataused to guide the movement of the sensing module or device; and theaccuracy and resolution of the tilt data used to guide the movement ofsensing module or device.

The starting location and orientation can be specified in many waysincluding physical examination, boney landmarks, imaging, and othermethods of identifying anatomical or anomalous features or structures onor within a patient's body. These approaches require an accurateestimate of the change in orientation and distance between the startingpoint and the final location and orientation for the probe, tool,instrument, or similar apparatus, or implants, prostheses or prostheticcomponents, at the target location.

A second alternative for estimating the location and orientation of thetarget location and orientation uses the motion and orientation sensingdevice to identify the center of rotation or alignment of a symptomaticlimb with respect to other joints or portions of the limb. The motionand orientation sensing device is then used to track the movement andorientation of the probe, instrument, alignment jigs or cutting blocks,instrument, or similar apparatus, or implants, prostheses or prostheticcomponents to guide them to the designated location and orientation.

A third approach to eliminating errors associated with estimating thedistance and change in orientation is to begin tracking the movement ofthe probe, instrument, or instrument having a motion and orientationsensing module or device precisely at the target location andorientation. In this case the objective is to return the probe orinstrument to exactly the same location and orientation it had when thetracking procedure was initiated. Starting and ending at the targetlocation and orientation may not be as limiting as it might firstappear. This procedure is applicable to many medical procedures whereinsomething is removed and replaced, or removed, modified, and returned toits original position and orientation. This includes many forms oftrialing. It also applies to any procedure wherein the same site on orwithin a patient's body is accessed two or more times during any medicalor surgical procedure.

Regardless of which method is used to establish the starting locationand orientation, as well as defining the distance to the target locationand its orientation, the sensing module or device can be used to trackeach incremental movement and change in orientation of probes,instruments, instruments, or similar apparatus. Each of these movementscan be captured accurately, and the location and orientation of thesensing module or device precisely updated in real time.

An additional variable arises whenever the target location may moveduring the tracking procedure. This can be caused by the patient'smovement, including movement as small as taking a breath. A markermotion and orientation sensing module or device can be attached to thepatient's body in a location that is fixed with respect to the targetlocation. Also, the orientation of the marker device can be fixed withrespect to the orientation of the target. When these conditions are metit is a straightforward process to update the target location andorientation whenever it is moved by applying the same software routinesthat update changes in the location and orientation of the trackingmotion and orientation module or device. The data from the trackingdevice may readily be adjusted to display the correct distance betweenit and the target, as well as its orientation relative to theorientation of the target, in real time.

The accuracy and resolution of the acceleration sensing elements iscritical to achieving the accuracy and resolution required to guide thesensing and tilt module or device. This includes both the accuracy andresolution of the sensing of acceleration as well as the tiltsensitivity of the acceleration sensors. These requirements are drivenby several attributes of intentional human motion in the areas of thetorso, arm, wrist, and hand. These determinative factors include therange of speed of intentional human arm and hand movements, thedexterity or fine motor control of the human arm, wrist, and handmovements, and the maximum frequency of intentional human arm and handmovements. The required tilt sensitivity of an accelerometer is alsodetermined by the parameters of human arm, wrist, and hand movements.

The maximum speed and frequency of human arm movements determines therequired measurement range of each accelerometer within a motion andorientation detection module or device. Small hand motions may includeacceleration levels up to 3 g. Vigorous motions may include accelerationlevels on the order of 4 g. Therefore an 8 g accelerometer will assurean adequate range of detection, even for a user with extremely high handspeed. An 8 g accelerometer may also enable the capture and analysis ofunexpected events such as dropping the probe, tool, instrument, orsimilar apparatus, or accidentally striking something with it.

The maximum speed and frequency of human arm movements is also adeterminative factor in the selection of the range and sample rate ofthe accelerometer or accelerometers and other circuitry within themotion and orientation detection module or device. Obviously the speedof human arm movements varies widely depending on the individual, aswell as speed with which a specific activity may be performed.

But the level of resolution required of the accelerometer oraccelerometers is independent of these differences. The level ofprecision required in medical procedures is the same regardless of howrapidly various individual movements may be performed by individualpractitioners. Therefore, although the measurement range of theaccelerometer or accelerometers can be set to the level required tocapture the most rapid applicable intentional human movements, this doesnot change the required level of resolution.

For many medical procedures the level of precision may be as small ashalf a millimeter. Therefore, a resolution of one-quarter millimeter, orless, may be required to assure this level of precision. The trackingelement (e.g., INS chip(s), accelerometer or accelerometers), and thecircuitry used for quantization, processing, and telemetry of position,velocity, acceleration and tilt data, must have this level ofresolution, when needed, to guide probes, instruments, instruments,alignment jigs or cutting blocks, or similar apparatuses, or probes,instruments, or instruments held in a physician's or caregiver's hand,or in a robotic arm and gripper, to the target with this level ofprecision regardless of the measurement range of the accelerometer oraccelerometers.

Intentional human movement tends to be limited to a maximum frequency inthe range of 10 to 12 Hz. A bandwidth of 40-60 Hz is adequate to capturethe detail of this range of motions.

A delicate medical or surgical procedure is obviously not performed atthe maximum speed a human arm or hand can move back and forth. Aconservative estimate for the maximum frequency of body motions in thesecases may be in the 5 Hz range. Sampling the output of the trackingelements (e.g., accelerometer or accelerometers, INS chip(s)) every 10milliseconds, or at a 100 Hz rate, will capture an average of 20 pointson a single cycle of a 5 Hz signal. This provides an adequate digitizedvirtual image of movements of this frequency or less.

In the discussion that follows, accelerometers will be used as anon-limiting example of a portion of a tracking element used to obtainpositional and orientation data. At the non-limiting example of a samplerate, discussed above (10 Hz), the effective least significant bitoutput by the accelerometer or accelerometers, as well as digitized bythe ADC circuitry and transmitted by the telemetry circuitry, mustprovide adequate resolution to support a precision level required forthe particular use, for example for certain surgical procedures ofone-half mm or less. Conservative estimates of the required resolutionof intentional motion during a medical procedure may include changes inlocation and orientation as small as a 0.1 millimeter. Intentionalmotion of movements this precise may also be as slow as 1 mm a second,especially when the probe, tool, instrument, alignment jigs or cuttingblocks, or probes, instruments, or instruments held in a physician's orcaregiver's hand are closing on the target.

When needed, the accelerometer or accelerometers, and the circuitry usedfor quantization, processing, and telemetry of acceleration and tiltdata, must have adequate resolution to guide probes, instruments,instruments, alignment jigs or cutting blocks, or similar apparatuses,or implants or prosthetic components to the target with this requiredlevel of precision.

Although the following discusses specific examples of the bitrequirement of data, other embodiments can use different bit levelsdepending upon the system requirements. The required number of bits maybe estimated based on the following assumptions: an 8 g accelerometer isa conservative range appropriate for capturing human motion duringmedical and surgical procedures, persons with the high levels ofdexterity required for medical and surgical procedures are capable ofprecise movements of their arm, wrist, and hand with a precision of lessthan ±0.5 millimeter, these persons also have steady control ofextraordinarily slow movements of their arm, and wrist, and hand to asslow as 1 mm a second, thus the levels of acceleration associated withslow movement of this level can be detected. Thus, the quantification ofmovements on this order can be represented by three or more bits. Thisprovides a resolution of approximately one tenth of the minimum level ofacceleration.

The results of the following analysis indicate that the resultingtechnical requirements are realistic and conservative, note that basingdesigns on highly conservative assumptions assures headroom to supportfuture advances in the gold standard of treatment for applicable medicaland surgical procedures.

Applying the standard equations:micro g=9.8066 micrometer/s2;Velocity in μm/s=time×Acceleration in μm/s2;1000 μm/s=1s(A μm/s2);Acceleration=1000 μm/s2=102 micro g;

Based on these equations and assumptions, reliable quantification of theminimum level of acceleration for exacting medical and surgicalprocedures with an 8 g accelerometer requires a minimum (EffectiveNumber Of Bits) ENOB of between 16 to 17 bits, or approximately 16.5binary bits of resolution. The term ‘effective number of bits,’ is afigure of merit that is calculated from signal-to-noise plus distortion(SINAD). A resolution of approximately one tenth of the minimum level ofacceleration is conservatively adequate. To have three or more bits ofadditional resolution at the minimum level of acceleration requires aneffective number of bits of 20. This is adequate for trackingintentional movement of the torso, arm, wrist, and hand motion definedduring exacting medical and surgical procedures.

The assumptions about intentional human movements may also be used as abasis for defining the required tilt sensitivity for guiding themovement of the motion and orientation sensing module or device. Aconservative assumption of tilt sensitivity requirements of anaccelerometer or accelerometers can be calculated by once again assuminga precision orientation requirement of ±0.1 millimeters with respect tothe central ±0.5 mm of the target orientation. The required precision ofthe least significant bit is approximately 980.66 micrometer/s2. For an8 g accelerometer this requires in an ENOB greater 17.5 to achieve aresolution of one-tenth of the minimum required resolution. Thisequivalent number of bits is less than the resolution required formotion detection. Therefore circuitry that adequately detects,quantizes, and processes motion data will be more than adequate for tiltdata as well.

A conservative assumption of sensitivity to yaw achieved by a pair oftriaxial accelerometers can be calculated based on the previousassumption of the precision of each accelerometer. This assumption maybe restated that each of the two triaxial accelerometers achieves aprecision of ±0.1 millimeters when used to calculate positionallocation, or slightly greater than ±4 mils. Applying this assumption, anexample device having two triaxial accelerometer die separated by oneinch, center to center, along the longitudinal axis of the motion andorientation sensing module or device can conservatively achieve aprecision in detection and quantization of yaw of 13.75 arcminutes.Therefore these assumptions on the precision of intentional humanmovements produce consistent results for detection and quantization ofyaw. Since the precision of measurements of relative distance andorientation is likely to be higher than absolute measurements,acceleration sensing elements and circuitry that adequately detects,quantizes, and processes movement data will be more than adequate foryaw data as well.

This estimated requirement of an ENOB of 20 is based on multiple worstcase assumptions. These assumptions include the worst case maximum andminimum rates of acceleration, the worst case maximum and minimum speedsof movement, and the worst case level of required precision for bothlinear movement and orientation. Obviously this is intended to maximizepatient safety as well as contribute to the achievement of highlyeffective outcomes of medical and surgical procedures.

Twenty bits of effective resolution is approximately one part permillion (ppm). Accuracy in the ppm range and requires high precisioncircuitry and components. The requirements of the design, production,and test of precision circuitry of this level of precision are wellunderstood and appropriate approaches are well developed in theelectronics industry. This level of resolution may help contribute tothe advancement of the precision, repeatability, and documentation ofcurrent manual approaches to controlling the movement and orientation ofprobes, instruments, instruments, alignment jigs or cutting blocks, orsimilar apparatus, or implants, prostheses or prosthetic components, inmedical procedures.

The model of human arm movement outlined here is also applicable torobotic arm movement as well. These movements, especially in thepresence of human participants, must not endanger humans within the spanof the robotic arm. Therefore constraining it to perform tasks withinthe limits of human movement may be a reasonable safety precaution. Ifthis constraint is not required, the requirements defined in thisdescription can readily be extrapolated to cover broader requirementsfor controlling the movement of a robotic arm and gripper. Also,operating a robotic arm and gripper, and the associated motion andorientation module or device, in servo mode can enable even greaterlevels of accuracy and precision. A robotically assisted extension ofsome medical and surgical procedures may enhance consistency of outcomesas some literature on robotic-assisted procedures asserts.

In addition to estimating the levels of acceleration and range offrequencies that must to be measured as well as the required samplingfrequency and resolution of measurements, determining the selectioncriteria for accelerometers and analog to digital converters (ADC)requires knowledge of accelerometer and analog to digital conversionoperations and performance. There are several types of accelerometers.Common types of accelerometers include: capacitive accelerometers andpiezoresistive accelerometers.

Capacitive accelerometers have a moveable micromachined feature thatacts as one side of a variable capacitor with respect to a fixedstructure within the integrated circuit die. Movement of the integratedcircuit causes displacement of this moveable structure resulting in achange in the level of capacitance that is proportional to acceleration,including gravity.

Piezoresistive accelerometers are based on a beam or micromachinedfeature whose resistance changes as it is flexed by movement of theproof mass. Movement of the proof mass is proportional to acceleration,including gravity.

Bulk MEMS capacitive and piezoresistive accelerometers can have some ofthe highest accuracy specifications of the commonly availableaccelerometer technologies for general linear accelerometerapplications.

Piezoelectric accelerometers are dynamic accelerometers having a crystalsensing element that emits a charge when compressed by movement of theproof mass.

Magnetoresistive accelerometers convert acceleration to an electricalsignal by measuring the resistance of a material whose resistivitychanges with changes in the surrounding magnetic field.

Hall Effect sensors convert acceleration to an electrical signal bysensing changes in the surrounding magnetic field.

A thermoelectric accelerometer uses heated gas molecules to detectacceleration. Thermocouples are placed opposite four sides of a heatsource suspended within a cavity. Under zero g, the temperature is thesame at all four thermocouples. Acceleration in any direction will causethe temperature profile to become asymmetrical creating differences inoutput voltages of individual thermocouples proportional to theacceleration.

An optoelectronic accelerometer uses an optical position sensor (OPS,)or position sensitive detector (PSD), to provide an analog outputvoltage from a photodiode surface that is proportional to the positionand movement of the centroid of a spot of light influenced by themovement of a proof mass.

An interferometric accelerometer detects the movement of the proof masswith an interferometric fiber optic sensor.

Microelectromechanical (MEMS) accelerometers are rugged, low cost andsmall in size. They may be discrete components or fabricated as eithersurface or bulk MEMS structures within integrated circuits. Theindividual outputs of each accelerometer integrated within an integratedcircuit die or multi-circuit package may be oriented along each of axisof the Cartesian coordinates. The output from these acceleration sensingstructures may be analog electrical parameters or signals, outputfrequencies, pulse interval modulation streams, or digital values froman analog to digital convertor. More complex integrated circuits mayinclude additional functions integrated within the individual integratedcircuit chip or die.

Just as an accelerometer converts physical acceleration into electricalsignals or changes in electrical parameters, the output of anaccelerometer can be converted into digital data that can be processedby logic circuits. Conversion from analog signals to digital or binaryvalues inherently involves comparator action where the value of theanalog voltage at some point in time is compared with some standard.Basic analog to digital conversion circuits include:successive-approximation; sigma-delta; flash, parallel, or directconversion; pipeline; digital ramp; and various implementations of slopeanalog to digital conversion circuits. Resolution is a criticalparameter that can drive the selection of specific analog to digitalconversion circuits in many applications. Another parameter that can becritical in some applications is sample frequency or conversion rates.Pipeline and flash ADCs may be selected for these applications.

Other functions can also be included within a motion and orientationsensing module or device. For wireless operation telemetry circuitry, ortelemetry circuit and antenna is required. Also, some form of controllogic is required to coordinate the operation of the circuitry andsensors to assure the data from the acceleration sensing structures istransmitted successfully to an external computer system. This controllogic may require inputs from the user and some form of touch sensitiveinput structures or functions are required. Obviously all these sensorsand circuitry require power to operate. Therefore a power source, suchas a battery or large-value capacitor, as well as some form of ON/OFF,START/STOP switching structure is required.

Critical factors that can affect the accuracy and resolution of themeasurement of acceleration and tilt include: mechanical instability andelectrical noise.

Mechanical instability or loose components or wiring can causemechanical noise that is picked up by an accelerometer, or can evenresult in erroneous or spurious movement of the acceleration sensorselement within an accelerometer, creating spurious acceleration and tiltdata.

Electrical noise can limit the ENOB of the data conversion processingchain composed of the acceleration sensors, conversion to digitalsignals, and interference affecting telemetry transmissions. ADCs andsignal conditioning circuitry may generate noise internally. Also crosstalk or digital circuitry may create noise on power supply conductorsshared with other circuitry.

High-precision analog semiconductor devices are sensitive to physicalstress at the die and packaged circuit levels.

Thermoelectric voltages, the Seebeck effect, can be generated atjunctions of dissimilar metals. Generated voltages can be as large as amillivolt for a change in temperature of one degree centigrade.

As with all precision circuits, drift of temperature sensitive elementswithin the electronic components and substrate can be a major source oferror.

Long-term stability can also be a factor affecting the performance ofhigh precision sensors and analog circuits as they undergo long-termage-related changes.

Variations in supply voltage can also affect the conversion of theamplitudes and directions of acceleration and tilt to binary outputs. Insome circuits a major potential for error in the analog to digitalconversion process is the lack of high-precision reference voltages.

Methods for addressing these issues are well defined. The evaluation andapplication of selected design approaches that can mitigate or eliminatethe impact of individual sources of inaccuracy and level of resolutionare well known and can support the attainment of ppm performance.

Motion and tilt sensing modules and devices must have high levels ofmechanical integrity. At least one embodiment is less than a cubiccentimeter, that expert mechanical design, mature electronicmanufacturing methods, and careful selection of materials used for thesubstrate and enclosure can assure the required level of mechanicalintegrity and stability. This includes securely mounting all components,the substrate, and all wiring so that accelerometers are only subjectedto external sources of motion or vibration.

Likewise the connection between the motion and orientation of thesensing module or device and the probe, tool, instrument, or similarapparatus it is attached to, affixed on, or embedded or integratedwithin, must have high integrity and stability. The small size alsofacilitates attaching motion and orientation module or device to,affixing it on, or embedding or integrating it within, a probe, tool,instrument, alignment jigs or cutting blocks, or other similarapparatus. It can then be calibrated to provide accurate data on themovement and orientation of the probe, instrument, or instrument whileit is moved to simulate worst case usage. This calibration informationcan be stored within the circuitry of the motion and orientation moduleor device and used in conjunction with an auto-calibration procedure toassure the required accuracy and precision.

Also, the mechanical design and manufacture of the substrate andenclosure must assure highly accurate orientation of the accelerationsensors within the motion and orientation sensing module or device. Toachieve the greatest resolution, the integrated circuit or circuitscontaining accelerometers can be mounted with the sensitive axes eitherparallel or normal to the plane of movement, depending on the mechanicaldesign of the sensor. Tilt measurements are also sensitive to theorientation of the sensor. These measurements are most sensitive whenthe accelerometer is in its 0 g orientation. As a DC accelerometer'ssensitive axis is tilted from pointing horizontal to vertical, theinfluence of gravity varies as a function of the sine of the anglebetween the horizon and the accelerometer's sensitive axis. Thereforeany errors in the mounting of DC accelerometers are highly significant.The substrate can be mounted within the motion and orientation sensingmodule or device for maximum sensitivity when it is in its finalposition on or within the instrument, probe, instrument, alignment jigsor cutting blocks, or similar apparatus.

In at least one embodiment noise reduction and noise canceling measurescan be included in the design. This includes incorporating filtering,dithering, oversampling, and decimation functions in the analog signalto digital code conversion process. The likelihood of an analog signalbeing exactly equal to a digital value is small. Therefore a combinationof dithering and oversampling is capable of developing an accurateestimate of the actual value of a point on an analog waveform to agreater level of resolution than direct sampling.

Only pure sine waves are harmonic free. Even then, non-linearity maycreate harmonics and intermodulation products. Therefore anti-aliasinglow-pass filtering is required to remove harmonic signals andintermodulation products and all other signals above the Nyquistfrequency that can introduce nonrandom distortions into the oversampled,dithered analog waveforms. Dithering an analog signal adds a white noiseor Gaussian noise component that creates a stochastic variable with amean value of zero for each sample of the analog waveform. Thecombination of dithering and oversampling enables the interpolation ofanalog values at each point on the analog waveform. Over-samplingincreases the number of discrete samples compromising the digitizedrepresentation of an analog waveform. The greater the sample rate of theanalog to digital conversion the more accurate the representation of theinput signal is when the oversampled digital values are recombined. Thissample rate may be as little as twice the Nyquist frequency as much as256 times the Nyquist frequency. For each desired additional bit ofresolution the analog signal can be oversampled by at least four times.

The oversampled analog-to-digital converted signal can be low-passfiltered to limit the effects of quantization noise without affecting DCaccuracy. Quantization noise is inherent in the analog to digitalconversion process. It is the result of the quantization process as itconverts a continuous waveform to discrete values. A low passquantization filter can also help attenuate higher frequency mechanicaland electrical noise and improve the overall signal to noise ratio ofthe physical acceleration to digital code conversion process.

Decimation is required to digitally down-sample the over-sampled digitalvalues by aggregating groups of over-sampled digital values with thenumber of digital values within each group depending on thedown-sampling divisor. Each down-sampled digital value is then rightshifted to scale the answer correctly to the increased level ofresolution required for the final high-resolution digital values.

The combination of anti-alias filtering, dithering, oversampling,quantization filtering, and decimation functions can extend theeffective number of bits (ENOB) of the data conversion chain linkingphysical acceleration to a digitized waveform by three or moreleast-significant-bits. This may be required to assure ppm resolution inthe analog to digital conversion process.

Well-designed electrical conductor widths, routing, partitioning, andshielding on and within the substrate also minimizes noise andcross-talk.

Expert design and good manufacturing process control minimizes the levelof physical stress placed on integrated circuit die and packaged devicesand eliminates this potential source of error.

The same is true for thermoelectric voltages created by the Seebeckeffect. The number of junctions of dissimilar metals, and the magnitudeof thermoelectric voltages created where junctions of dissimilar metalsmust interface, is minimized by appropriate selection of materials andelectronic assembly methods.

Changes in the temperature of the environment of the motion andorientation sensing module or device when it is in operation areminimal. First, the environment within operating rooms or other sectionsof healthcare facility are carefully maintained. Second, the powerconsumption of the motion and orientation sensing module or device isvery low and does not materially raise its operating temperature. Thesetwo factors minimize the changes in temperature of sensitive componentsand effectively eliminate temperature drift as a source of error duringthe relatively brief time the motion and orientation sensing module ordevice is active.

Applications wherein the starting location and orientation may be usedas the target location and orientation provides a substantial advantagein tracking the progress of the motion and orientation sensing module ordevice. In these applications the sum of distances traveled in all threeaxes is zero and the sum of changes in orientation in all three axes isalso zero, the relative values of acceleration and tilt are morecritical, and the absolute values of acceleration are less critical.This greatly reduces the impact of many of the factors that canadversely impact the accuracy and precision of the conversion ofphysical acceleration to digital values.

Achieving relative accuracy with high levels of resolution is moretractable because even if precision components and circuits, as well asreference and supply voltages, drift slowly over time this will notadversely impact the accuracy, or effective number of bits required forrelative measurement results. Therefore aging and temperature changesare not major deterrents to ppm performance of the motion andorientation sensing module or device during the relatively brief timethe motion and orientation sensing module or device is active.

Furthermore, precision electronic sensors and components do not agerapidly enough for aging to be a factor in their performance within thetime required for an individual surgical or medical procedure. Also,because of sterility requirements in medical procedures and facilities,the motion and orientation sensing modules and devices are limited tosingle-use in many applications.

In addition to the accuracy and resolution of the conversion ofacceleration into electrical signals, the accuracy and resolution of theconversion of analog voltage to digital values is key determinate of theENOB. The performance of ADC circuits is dependent on many factors.Specifications for the various forms of noise, offset, gain, andlinearity specifications are all critical to achieve ppm performance andcan be thoroughly reviewed.

A conservative estimate of the requirements for the application ofaccelerometer technologies for medical applications indicates theseaccelerometers must detect changes of one millionth of the totalcapacitance or resistance respectively. Repeatable ppm sensitivity, withno missing codes, in an 8 g accelerometer is required to achieve an ENOBof 20. This requires the application of multiple measures for enhancingthe performance of accelerometers, analog to digital converters, andreference voltages, including: High resolution capacitive orpiezoresistive accelerometers, or a force-balance, force-feedback, orservo mode operation of variable capacitor accelerometers.

Ratiometric operation incorporated into accelerometer and ADC circuitsfacilitates the conversion of changes in acceleration and tilt intobinary outputs that are independent of drift and variations in supplyand reference voltages. Sigma-delta analog to digital conversion canalso be used in the ADC circuitry.

The complete analog to digital conversion process can incorporate lowpass anti-alias and quantization filtering, dithering, oversampling, anddecimation functions in the conversion of physical acceleration tobinary outputs with the effective number of bits to achieve ppmresolution. Chopper stabilization of the ADC inputs can also minimizeoffset and drift.

Executing an automatic calibration procedure as the circuitry ispowered-up can mitigate offset and gain errors, aging or temperaturesensitivities of the sensors and electronic circuitry, as well asconfirming the noise floor and battery voltage and charge of the motionand orientation sensing module or device.

In addition to the level of integration of the acceleration sensors andcircuitry, there is also a range of possible software functions that maybe integrated into an individual motion and orientation sensor module ordevice. These features include detection of several exceptionconditions, including: free-fall, tumbling, spinning, shock, and tap anddouble tap. In addition to the accelerometer or accelerometers and ADC,filtering or digital signal processing circuitry can be used to detectand quantize the signals necessary for these additional functions. Thiscan include low pass and high pass filters to discriminate among varioustypes of exception condition signals.

Free-fall detection will alert the computer system, and the user, if themotion and orientation sensor module or device is dropped. A free-fallcondition is detected whenever the static acceleration average output ofall three acceleration sensing elements drops to zero or g. Output fromthe accelerometers may still have cyclic dynamic output. This mayindicate the motion and orientation sensing module or device is alsotumbling or spinning while it is falling. Whenever any of theseconditions are detected, it can indicate the need to reset and restartthe tracking procedure.

A physical transient or shock is detected whenever a high frequencydynamic acceleration signal exceeds a pre-set level in one or more axes.Transient detection is based on signals from a high pass filter thatfilters out static acceleration and low speed acceleration signals. Thismay indicate the probe, instrument, or instrument has been subjected tomechanical shock such as striking, or been struck by, a solid object. Itmay be appropriate to reset and restart the tracking procedure afterthis condition is detected as well.

Obviously acceleration sensors may also be used to detect tap and doubletaps on the motion and orientation sensing module or device, or theprobe, instrument, or instrument. This capability may enable the surgeonto give START and STOP commands without removing his or her hands fromthe probe, instrument, or instrument.

These examples of software functions that can be used to leverage theflow of information available from the dynamic and static sensing ofacceleration and tilt illustrate the significant real-time utilityavailable, not only by detecting and tracking motion and orientation,but by analyzing its features in real time. Leveraging thesecapabilities maximizes the information content of these data streams.

There are many possible applications of motion and orientation sensingmodules or devices in medical and surgical procedures. For example, thebenefit of trialing may be enhanced by the use of a tracking motion andorientation sensing module or device. The addition of a second markermotion and orientation sensing module or device may improve the accuracyand resolution of the replacement of a measurement instrument, trialinsert, or prosthetic component if there is any possibility of evenmicroscopic movement by the patient. Data from this market module ordevice is used to track movement and changes in orientation of thetarget. Within a trialing application the tracking motion andorientation sensing modules or devices may be used to track theretraction of a measurement instrument, trial insert, or prostheticcomponent. The same motion and orientation sensing module or device canthen be used to guide the positioning and orientation of the chronicimplant device in various orthopedic procedures. For example, a spinaldisk replacement procedure, or a prosthetic implant in any joint, areexamples that illustrate the application of motion and orientationsensing modules or devices to guide the movement and orientation of amedical instrument. There are multiple methods a chronic implant mightbe guided back to the precise location and orientation identified withthe use of a measurement instrument, trial insert, or prostheses orprosthetic component.

Possible approaches can include: a single instrument that preciselygrips different trial inserts, or prostheses or prosthetic components,as well as the final implant, attaching the same motion and orientationsensing module or device to different identical instruments with eachone specialized to hold different sized trial inserts as well as thefinal implant, two instruments, each having a separate motion andorientation device. One instrument optimized for holding trial insertsor prostheses or prosthetic components, and a second instrumentoptimized for holding the chronic implant. When the instruments areplaced in precise physical contact a signal is generated and thecomputer software computes the location and orientation of the secondinstrument based on the location and orientation of the firstinstrument.

The addition of a motion and orientation sensing module or device to ageneric instrument illustrates how it may be used to assist in guidingthe positioning and orienting the replacement disk accurately within apatient's spine. In addition to a generic instrument having a motion andorientation sensing device, this example also illustrates the rolecomputer hardware and software provide to the development of a systemssolution. If the implant site in this example application cannot beassured to be absolutely fixed, a second, marker, motion and orientationsensing device can be pinned to the patient's body near enough to theimplant site that its position and orientation are fixed with respect tothe site of the implant. The data from this second device can be used toadjust the target location so it continues to accurately correspond withthe implant site even if it is moving slightly. This will assure theaccuracy of the positioning and orientating of the implant within therequired level of precision.

Various example embodiments of example motion and orientation sensingmodules or devices, an example application of a disk replacementprocedure, example flowcharts of an example approach to the process androle of software within the procedure, as well as example computerdisplay images, are illustrated in the following figures.

The following figures will be used to describe non-limiting examples ofa subset of possible embodiments. FIG. 1 is a simplified view 2000 of aphysician holding an embodiment of a surgical tracking system includinga motion and orientation sensing device (e.g., a surgical device holderportion of a surgical tracking system) with a computer display (e.g., asurgical tracking display system) of its location and orientation atsome distance from a pre-specified target. FIG. 1 illustrates the use ofreal-time data from an example wireless motion and orientation sensingdevice to provide real-time visual feedback to aid a physician to guidea medical probe or instrument to a predefined location and contactingthat location at a predefined orientation. In this example a sagittalview of knee joint 2004 is used as an illustration of an anatomicalfeature defining a target location and orientation. Computer display2016, connected to computer 2014 (optionally including a processor thatcan process tracking data), having computer keyboard 2010 and computermouse 2012, displays image 2020 of a target location within knee joint2004. Computer display 2016 also displays image 2018 of the targetorientation within knee joint 2004. For example physician 2002 holds amedical instrument 2008 (surgical device) having an example embodimentof a motion and orientation sensing device 2006 (surgical deviceholder). Physician 2002 is prepared to move instrument 2008 to thetarget location and orientation within knee joint 2004. The exampleembodiment of a motion and orientation sensing device 2006 detects,quantizes, and transmits movement, tilt, and yaw data to computer 2014(e.g., the computer display of a surgical tracking display system). Thisdata will begin updating images 2018, 2020 on display screen 2016 asphysician 2002 begins to move instrument 2008.

FIG. 2 is a simplified view 2100 of a physician holding an embodiment ofa surgical tracking system including a motion and orientation sensingdevice (e.g., surgical device holder) with a computer display (e.g., thecomputer display of a surgical tracking display system) of its locationand orientation approaching a pre-specified target. FIG. 2 illustratesthe use of tracking data from an example wireless motion and orientationsensing device to provide real-time visual feedback to aid a physicianto guide a medical probe or instrument to a predefined location andcontacting that location at a predefined orientation. In this exampleknee joint 2004 is used as an illustration of an anatomical featurehaving an example a target location and orientation. Computer display2016, connected to computer 2014, having computer keyboard 2010 andcomputer mouse 2012, displays image 2120 of the target location withinknee joint 2004. Computer display 2016 also displays an image 2118 ofthe target orientation within knee joint 2204. Example physician 2002holds an example medical instrument 2008 having an example embodiment ofa motion and orientation sensing device 2006 that detects, quantizes,and transmits movement, tilt, and yaw data to computer 2014. Asphysician 2002 moves example medical instrument 2008 motion andorientation sensing device 2006 transmits tracking data to computer2014. Images of relative orientation 2118 and location 2120 on computerdisplay 2016 are updated in real time. This enables physician 2002 tojudge the difference in location and orientation between instrument 2008and the target location and orientation within knee joint 2004 while heor she continues to move instrument 2008. Updates of images 2118, 2120on computer display 2016 continually reflect the movement of medicalinstrument 2008 until it reaches the target location and orientationwith the patient's knee 2004. The combination of motion and orientationsensing device 2006 and real-time updates of images 2118 and 2120 oncomputer display 2016 aids a user (e.g. physician) 2002 to accuratelyguide instrument 2008 precisely to the target location and orientationwithin knee joint 2204.

FIG. 3 is a simplified view 2200 of a physician holding an embodiment ofa surgical tracking system including a motion and orientation sensingdevice with a computer display defining its location and orientation atsome distance from a pre-specified target plus a second motion andorientation sensing device pinned to a patient to track any movement ofthe target. FIG. 3 illustrates the use of real-time data from twoexample wireless motion and orientation sensing devices to providereal-time visual feedback to aid a physician to guide a medical probe orinstrument to a predefined relative location and contacting thatlocation at a predefined relative orientation. In this example asagittal view spine 2204 is used as an illustration of an anatomicalfeature having a possible target location and orientation 2222. Examplephysician 2202 holds example medical instrument 2208 (e.g., surgicaldevice) having an example embodiment of a motion and orientation sensingdevice 2006. In a second embodiment a marker motion and orientationsensing device 2223 is affixed to the body of patient 2224 in a fixedposition and orientation with respect to target location and orientation2222, providing movement information that will affect the position andorientation of the target location. Computer display 2016, connected tocomputer 2014, having computer keyboard 2010 and computer mouse 2012,displays image 2220 of the distance between instrument 2208 and targetlocation 2222 on spine 2204. Computer display 2016 also displays image2218 of the difference between the orientation of instrument 2208 andthe orientation of target location 2222. Physician 2202 is prepared tomove instrument 2008 to the target location and orientation 2222 withinspine 2204. The example embodiments of motion and orientation sensingdevices 2006, 2223 will detect, quantize, and transmit movement, tilt,and yaw data to computer 2014. Images 2218, 2220 on display screen 2016can be updated in real time as physician 2202 begins to move instrument2008.

FIG. 4 is a simplified view 2300 of a physician holding an instrumenthaving an embodiment of a motion and orientation sensing device with acomputer display defining its location and orientation approaching apre-specified target while a second motion and orientation sensingdevice pinned to a patient tracks any movement of the target. FIG. 4illustrates the use of real-time data from two example wireless motionand orientation sensing devices to provide real-time visual feedback toaid a physician to guide a medical probe or instrument to a predefinedrelative and contacting that location at a predefined orientation. Inthis example a sagittal view of spine 2204 is used as an illustration ofan anatomical feature having an example target location 2222. Examplephysician 2202 holds example medical instrument 2208 having an exampleembodiment of a motion and orientation sensing device 2006. The exampleembodiment of a tracking motion and orientation sensing device 2006detects, quantizes, and transmits acceleration, tilt, and yaw data tocomputer 2014 in real time as physician 2202 moves example medicalinstrument 2208. Simultaneously, example embodiment of a marker motionand orientation sensing device 2223 detects, quantizes, and transmitsacceleration, tilt, and yaw data to computer 2014 in real time as spine2204 of patient 2224 moves, even microscopically. Computer display 2016,connected to computer 2014, having computer keyboard 2010 and computermouse 2012, displays image 2320 of the relative position of instrument2208 with respect to target location 2222 on spine 2204. Computerdisplay 2016 also displays image 2318 of the relative orientation ofinstrument 2208 with respect to the orientation of target location 2222.The images of the target location 2320 and the orientation of the target2318 on display screen 2016 are updated in real time with data fromexample marker motion and orientation sensing device 2223. Updatingimage 2320 in real time with data collected from both example motion andorientation sensing devices 2006, 2223 enables physician 2202 toaccurately judge the distance between the leading edge of instrument2208 and target location 2222 even if the target location is notabsolutely fixed. Simultaneously, updating image 2318 in real time withdata collected from both example motion and orientation sensing devices2006, 2223 enables physician 2202 to accurately judge the difference inorientation between instrument 2208 and target location 2222 even if thetarget location is not fixed. The combination of example motion andorientation sensing devices 2006, 2223 and real-time updates of images2318 and 2320 on computer display 2016 aids physician 2202 to accuratelyguide instrument 2208 to target location 2222 within spine 2204 with therequired orientation and precision even if target location is fixed ormoving slowly or slightly.

FIG. 5 is a simplified perspective view 2400 of an example of a motionand orientation sensing device, a cover for the device, and aninstrument into which a motion and orientation sensing device may beplaced. FIG. 5 illustrates a simplified perspective exploded view of anexample medical instrument and an example motion and orientation sensingdevice, prior to assembly. The example motion and orientation sensingdevice 2006 detects, quantizes, and transmits data defining themovement, tilt, and yaw of example medical instrument 2402. In thisexploded view of example medical instrument 2402 having cavity 2404 andcover 2414 sized to hold example motion and orientation sensing device2006 securely within its handle 2406. When assembled, example medicalinstrument 2402 having shaft 2408 and coupling 2410 may be used to trackthe movement and orientation of example medical inserts or prostheticcomponents or implants held in interchangeable heads mounted on coupling2410.

FIG. 6A is a simplified perspective view 2500 of an example instrumenthaving an example motion and orientation sensing device, a cover for thedevice, an interchangeable head, and an example insert or implant thatmay be held by the instrument. FIG. 6A illustrates a simplifiedperspective exploded view of an example medical instrument prior toassembly with an example motion and orientation sensing device,interchangeable head, and example medical insert or prosthetic componentor implant. The example motion and orientation sensing device 2006detects, quantizes, and transmits data defining the movement, tilt, andyaw of an example medical insert, implant, prosthetic component orprostheses 2518. In this exploded view of example medical instrument2402 having cavity 2404 and cover 2414 sized to hold example motion andorientation sensing device 2006 securely within its handle 2406. Exampleinterchangeable head 2516 may be attached to medical instrument 2402 byplugging its base onto coupling 2410 on the end of shaft 2408. Exampleinterchangeable head 2516 may be used to hold example medical inserts,prosthetic components, prostheses, or implants 2518. This completedassembly may be used to track the movement and orientation of an examplemedical example medical insert, prosthetic component, prostheses, orimplant 2518 in real time.

FIG. 6B illustrates a simplified perspective view of an assembledexample medical instrument having an example motion and orientationsensing device for tracking its movement and orientation, aninterchangeable head, and an example medical insert or prostheticcomponent or implant held by the instrument. When assembled the medicalinstrument 2402 having example motion and orientation sensing device2006 may be used to track the movement and changes in orientation ofexample medical insert, prosthetic component, prostheses, or implant2518. The example motion and orientation sensing device 2006 detects,quantizes, and transmits data defining the movement, tilt, and yaw ofexample medical insert, prosthetic component, prostheses, or implant2518 in real time. Example medical instrument 2402 having handle 2406and shaft 2408, plus cover 2414 securing example motion and orientationsensing device 2006, may be used to track changes in the location andorientation of medical insert, prosthetic component, prostheses, orimplant 2518 when positioned securely 2520 within interchangeable head2516.

FIG. 7 is a simplified example top-level flow chart of the stepsperformed by an example system having an embodiment of the motion andorientation sensing module or device and a computer system for guidingan instrument to return to its initial position. FIG. 7 illustrates asimplified example flow chart of the steps performed by an examplesystem having an embodiment of the motion and orientation sensing moduleor device with a real-time display to aid a user in guiding a probe,instrument, alignment jigs or cutting blocks, or similar apparatushaving a motion and orientation sensing module or device integrated orembedded into, affixed onto, or attached to it. The instrument may belocally or remotely controlled to accurately orient and position itsactive tip or member to return precisely to its initial position andorientation. If a second, or marker, example motion and orientationsensing device is positioned to track any change in location ororientation of the target, that device will be referred to as a ‘markerdevice’ and the motion and orientation sensing module or device used fortracking movement and changes in orientation of a probe, tool,instrument, alignment jigs or cutting blocks, or similar apparatus willbe referred to as a ‘tracking device.’ The relationships among the ninetop-level functions required to perform the tracking procedure includeactions by the user, processes executed by the motion and orientationsensing module or device, and software procedures executed by thecomputer system.

In step 2600 a top level software transfers control to subordinateroutines and functions as required to perform the tracking procedure.

In step 2602 the user prepares for tracking a probe, tool, instrument,or alignment jigs or cutting blocks, or similar apparatus, by definingthe target location and orientation, and powering the motion andorientation sensing module or device 2700. Powering-up the motion andorientation sensing module or device may be as simple as pressing aSTART button or icon, or double-tapping the handle of the case of themotion and orientation sensing module or device or the handle of theassociated probe, tool, instrument, or alignment jigs or cutting blocks,or similar apparatus.

In step 2604 control is transferred to the motion and orientationsensing module or device to execute its power up procedure 2800 andtransmit the results to the computer.

In step 2606 control is transferred to software routine 2900 thatdirects the example motion and orientation sensing module or device toquantify and transmit the initial orientation tracking data point andthe corresponding static acceleration of gravity to the computer.

In step 2608 control is transferred to software routine 3000 thatdirects the example motion and orientation sensing module or device todetect initial movement and transmit the second tracking data point tothe computer.

In step 2610 control is transferred to software routine 3100 thatdirects the example motion and orientation sensing module or device todetect and transmit tracking data for motion and orientation samples twothrough one-hundred to the computer.

In step 2612 control is transferred to software routine 3200 thatdirects the computer to calculate and display the trajectory andorientation of the motion and orientation sensing module or devicethrough the first one hundred data tracking points.

In step 2614 control is transferred to software routine 3300 thatcalculates and displays the trajectory and orientation of the motion andorientation sensing module or device through each additional successivemovement and orientation data point.

In step 2616 if the motion and orientation sensing module or devicedetects an exception condition it signals an alarm that triggers analert by the computer. Also, if the user elects to stop tracking, or thetracking procedure is completed, needs to be restarted, or can beaborted, control is transferred to the exception processing routine3500.

FIG. 8 illustrates a simplified example flow chart of the stepsperformed by a physician, surgeon, or other user preparing to use anexample embodiment of the motion and orientation sensing module ordevice to guide a medical instrument to return to its initial locationand orientation.

In step 2700 the user is alerted by the computer display that thecontrol software is in the proper state for the preparation of theexample motion and orientation sensing module or device.

In step 2702 the user begins the preparations for tracking a probe,instrument, alignment jigs or cutting blocks, or similar apparatus byidentifying the target location and orientation. The user selects theappropriate probe, instrument, or similar apparatus for the procedure tobe performed and prepares it for its role in the procedure. The useralso prepares to apply the motion and orientation sensing module ordevice positioned, affixed, or integrated on or within the probe,instrument, or similar apparatus.

In step 2704 the user powers up the motion and orientation sensingmodule or device when it is attached or affixed to, embedded in, orintegrated with the appropriate probe, instrument, alignment jigs orcutting blocks, or similar apparatus. The user confirms the computer,telemetry receiver, and motion and orientation sensing module or deviceare powered up and ready to use. Powering up the motion and orientationsensing module or modules or device or devices may be as simple aspressing a POWER button or icon on the handle or case of each motion andorientation sensing module or device or tapping the handle of theassociated instrument.

In step 2706 the user checks the screen of the computer and confirmsthat the telemetry link between the computer and each motion andorientation sensing module or device is operational.

In step 2708 the user checks the screen of the computer and confirmsthat each motion and orientation sensing module or device has adequatebattery voltage and charge, the temperature is within elements, theauto-calibration procedure was successful, and the identification codeis correct.

In step 2710 the user inputs initial audio, graphic, annotations, notes,attachments, and other information into the electronic health recordbeing assembled on the computer for this procedure on this patient.

In step 2712 the user positions the instrument, and the marker device ifone is needed, in the desired locations and orientations and initiatestracking. Initiating tracking may be as simple as pressing each STARTbutton or icon a second time, or double-tapping the handle of the handleof the instrument a second time.

In step 2714 the user withdraws the instrument from the selected targetlocation and orientation after confirming that the target location andorientation has registered with the computer. The user continuallymonitors the computer display for any alarm conditions and taking anyappropriate actions or entering appropriate instructions or data to thecomputer as required.

In step 2716 the user moves the instrument to its interim position whilecontinuing to monitor the computer display for any alarm conditions andtaking any appropriate actions or entering appropriate instructions ordata to the computer as required.

In step 2718 the user makes the prescribed adjustments, changes, orreplacements to the instrument or its payload while continuing tomonitor the computer display for any alarm conditions and taking anyappropriate actions or entering appropriate instructions or data to thecomputer as required.

In step 2720 the user moves the instrument back to its initial positionand performs the prescribed actions at the target location andorientation while continuing to monitor the computer display for anyalarm conditions and taking any appropriate actions or enteringappropriate instructions or data to the computer as required.

In step 2722 the user terminates tracking with a STOP button, icon, ordouble tap on the motion and orientation sensing module or device ortapping the handle of the instrument. This transfers control to theException Processing routine 3500. Within that procedure the user inputsany final audio, graphic, annotations, notes, attachments, and otherinformation into the electronic health record assembled by the computerand stores the file in the appropriate database and execution of thetracking procedure is terminated.

FIG. 9 is a simplified example flow chart of the steps performed by anexample embodiment of the motion and orientation sensing module toprepare for tracking of changes in its location and orientation. FIG. 9illustrates a simplified example flow chart of the steps performed by anexample embodiment of each motion and orientation sensing module ordevice to prepare for tracking changes in its location and orientation.An automatic calibration procedure is executed whenever power is appliedto each motion and orientation sensing module or device. This assuresthe accuracy of accelerometers by assuring there is no offset voltageunder 0 g conditions. It also uses the acceleration of gravity as asecond calibration point for confirming scale parameters. This assuresthe accuracy of the sensing, conversion, and transmission ofacceleration and tilt in all three axes. The effects of offset and gainerrors in the ADC are also addressed by the automatic calibrationroutine. Confirming operating temperature, reference voltage, andadequate power level during the start-up of each motion and orientationsensing module or device minimizes the risk of inaccuracies orinconsistent tracking operation.

Whenever a motion and orientation sensing module or device is switchedon power-up procedure 2800 is executed. This includes the steps: 2802the battery voltage and level of charge within each motion andorientation sensing module or device are measured; 2804 each motion andorientation sensing module or device transmits an initial telemetrysignal to the telemetry receiver connected to the computer; 2806 doesthe computer display confirm reception of each initial telemetry signal?If not, go to step 2812. This will result in the conditional expressionat step 2812 to fail and control will be transferred to the ExceptionProcessing routine 3500. Then 2808 the temperature within each motionand orientation sensing module or device is measured; 2810 theauto-calibration routine within each motion and orientation sensingmodule or device is executed; and the control is transferred to step2812 to confirm correct results for all start-up tests. In step 2812Battery voltage and charge, temperature, and calibration results arechecked against specification to assure reliable operation of eachmotion and orientation sensing module or device. If all measurementshave the required values and telemetry is functional control istransferred to step 2818.

In step 2814 if one or more measurements did not have the requiredvalues, an error code is transmitted to the telemetry receiver connectedto the computer defining the exception condition that has been detected.If the failure condition results from failure to establish a telemetrylink this step will execute without any effect on the computer display.

In step 2816 control is transferred to the Exception Processing routine3500.

In step 2818 if all measurements are within limits, the calibrationconstants for each motion and orientation module or device are updatedand stored in nonvolatile memory within each device.

In step 2820 the data and device ID code of each motion and orientationmodule or device are transmitted to the computer.

In step 2822 control is returned to the control program at step 2606.The tracking procedure is now ready to begin as soon as the computersystem displays the necessary data for the user to verify the ID codes.

FIG. 10 is a simplified example flow chart of the steps performed by acomputer to capture the initial orientation data point and staticacceleration of gravity corresponding to that orientation from anexample embodiment of the motion and orientation sensing module ordevice.

In step 2900 control is transferred to the software routine thatperforms the necessary actions to capture the data point defining theinitial orientation of an example probe, tool, instrument, or alignmentjigs or cutting blocks, or similar apparatus and a marker motion andorientation sensing module or device.

In step 2902 the computer software monitors the output of the telemetryreceiver for the command to initiate capturing accelerometer datatransmitted by the tracking motion and orientation sensing module ordevice. The data defining the tilt in the gravity-sensitive axes of eachmotion and orientation sensing module or device are transferred throughthe telemetry receiver.

In step 2904 when the command to initiate the data capturing procedureis received the software proceeds to the next step 2906.

In step 2906 the computer screen displays a request for the user toenter any initial audio, graphic, annotations, notes, attachments, orother data input. An electronic health record is opened and all forms ofthe data input by the user are stored with the appropriate identifiersand tags.

In step 2908 each motion and orientation sensing module or device startssampling the static acceleration of gravity data defining tilt and thestrength of the corresponding static acceleration from eachaccelerometer sensing element of the triaxial accelerometers. Thesoftware updates the calculated averages of this data for eachadditional sample. Published values of the acceleration of gravity arenot used for estimating the static component of the accelerometerreadings because the actual acceleration of gravity is specific togeographic location on the surface of the earth.

In step 2910 if the sigma values of the averages of the tilt and staticacceleration are too large to achieve the required precision of theinitial tilt and static acceleration values, control is returned to step2908. When the sigma values of the averages of the tilt and staticacceleration achieve the required precision of the initial tilt andstatic acceleration control is transferred to step 2912.

In step 2912 the data defining the tilt of the tracking motion andorientation sensing module or device is stored in the orientation dataarray of the tracking software. This data may be adjusted with respectto the tilt of the tracking motion and orientation sensing module ordevice if a second, marker, example motion and orientation sensingdevice is active. The adjusted data from the tracking and markingdevices are stored.

In step 2914 the values of the strength of static acceleration on eachCartesian axis is stored and subsequent samples of acceleration data areadjusted to estimate the dynamic acceleration during each sample period.Because the initial location defines the target location, the dynamicacceleration and the location values of each device are set to zero foreach of the Cartesian coordinates aligned with the zenith and tangentsto the surface of the earth. This data for the tracking module or deviceis stored in the acceleration data and location data arrays of thetracking software. The initial location of the marker device is alsoassumed to be 0,0,0 if one is in use.

In step 2916 the computer screen is updated to display the orientationthe target location with the image of the instrument having the motionand orientation sensing module or device centered on that display.

In step 2918 the software examines the telemetry data to determine if aSTOP command has been received or an exception condition detected.

In step 2920 whenever a STOP command or exception condition has beendetected, control is passed to the Exception Processing routine 3500.

In step 2922 if no STOP command has been received and no exceptioncondition detected, the control is returned to the top level of thetracking software program at step 2608.

FIG. 11 is a simplified example flow chart of the steps performed by acomputer to capture the distance and direction of the initial movementof an example embodiment of the motion and orientation sensing module ordevice.

In step 3000 control is transferred to the software routine thatperforms the necessary actions to capture the second data point definingthe initial movement and the resulting location and orientation of anexample probe, tool, instrument, or alignment jigs or cutting blocks, orsimilar apparatus.

In step 3002 the data defining the acceleration in all three Cartesianaxes of each motion and orientation sensing module or device withrespect to the zenith and tangents to the surface of the earth aretransferred to the computer through the telemetry receiver. If a second,or marker, example motion and orientation sensing device is positionedto track any change in location or orientation of the target, theacceleration data may be adjusted for any changes in the location andorientation of the target before the tracking data is stored.

In step 3004 the data defining the orientation of the motion andorientation sensing module or device in all three Cartesian axes isstored in the orientation data array. If a second, or marker, examplemotion and orientation sensing device is active, the orientation datamay be adjusted for any changes in the orientation of the target beforethe tracking data is stored.

In step 3006 the adjusted data defining the level of dynamicacceleration along each Cartesian axis are stored in the accelerationdata array. The net average velocity along each Cartesian axis iscalculated for the duration of each sample interval. If a second, ormarker, example motion and orientation sensing device is positioned totrack any change in location or orientation of the target, this netaverage velocity may be net of any changes in the location ororientation of the marker device. The calculated average net velocity ofthe tracking device with respect to any movement of the target is storedin the velocity data array.

In step 3008 the net change in distance traveled along each Cartesianaxis during each sample interval is calculated and stored in thelocation data array. If a second, or marker, example motion andorientation sensing device is positioned to track any change in locationor orientation of the target, this net average velocity will be net ofany changes in the location or orientation of the target as well.

In step 3010 the software examines the telemetry data to determine if aSTOP command has been received and also checks if an exception conditionhas been detected.

In step 3012 whenever a STOP command is received, or an exceptioncondition has been detected, control is passed to Exception Processingroutine 3500.

In step 3014 if no STOP command has been received or exception conditiondetected the computer returns control to the top level of the trackingsoftware program at step 2610.

FIG. 12 illustrates a simplified example flow chart of the stepsperformed by the motion and orientation sensing module or device inconjunction with the computer to capture the initial 100 movements of anexample embodiment of the tracking motion and orientation sensing moduleor device.

In step 3100 control is transferred to the software routine thatperforms the necessary actions to collect data points 2 through 100defining the movement, location, and orientation of an example probe,tool, instrument, or alignment jigs or cutting blocks, or similarapparatus. If a marker device is active, the data may be adjusted basedon movement or changes in orientation of the target.

In step 3102 each motion and orientation sensing module or devicesamples the dynamic accelerometer data every 10 milliseconds.

In step 3104 the dynamic acceleration and tilt data in all threeCartesian axes, defined with respect to the zenith and tangents to thesurface of the earth, of the tracking motion and orientation sensingmodule or device are transferred to the computer through the telemetryreceiver. If there is an example marker motion and orientation sensingdevice, data from tracking device may be adjusted to account for anymovement or change in the location or orientation of the target beforethe data are transmitted.

In step 3106 the data defining the net levels of dynamic accelerationand tilt of the example tracking motion and orientation sensing moduleor device in all three Cartesian axes is stored in the acceleration andorientation data arrays. If an example marker motion and orientationsensing device is used in the procedure, the dynamic acceleration andorientation data can be adjusted for any changes in the location andorientation of the target.

In step 3108 the data defining the net average velocity along eachCartesian axis is calculated for the duration of each sample interval.The calculated average net velocity is stored in the velocity dataarray.

In step 3110 the net change in distance traveled along each Cartesianaxis during each sample interval is calculated and stored in thelocation data array.

In step 3112 the software examines the telemetry data to determine if aSTOP command has been received or the time without receiving data fromthe telemetry receiver has been exceeded.

In step 3114 whenever a timeout or other exception condition isdetected, or the STOP command is received, control is passed to theException Processing routine 3500.

In step 3116 if all 100 tracking data points have not been captured,control is transferred to step 3102 to continue sampling theaccelerometer data.

In step 3118 if no STOP command has been received, or exceptioncondition detected, the computer returns control to the top level of thetracking software routine at step 2612.

FIG. 13 is a simplified example flow chart of the steps performed by acomputer to analyze and display the initial 100 movements and changes inorientation of an example embodiment of the motion and orientationsensing module or device.

In step 3200 control is transferred to the software routine thatperforms the necessary actions to analyze and display the first 100 datapoints defining the movement, location, and orientation of an exampleprobe, tool, instrument, or alignment jigs or cutting blocks, or similarapparatus.

In step 3202 the distance between the active end of the instrument andthe target location is calculated by the computer for each sample datapoint and stored in the distance array. If a second, or marker, examplemotion and orientation sensing device is positioned to track any changein location or orientation of the target, the location data maypreviously have been adjusted for any changes in the location of thetarget before the real-time display is updated.

In step 3204 the computer calculates and stores the difference oforientation between the active end of the instrument and the targetorientation in the orientation array. If a second, or marker, examplemotion and orientation sensing device is positioned to track any changein orientation of the target, the orientation data may previously havebeen adjusted for any changes in the orientation of the target beforethe real-time display is updated.

In step 3206 if the net distance less than 5-percent of the scale of thedisplay the display can be re-scaled to improve the visibility of therelative locations and orientations of the instrument and the target.

In step 3208 if the net distance greater than 50-percent of the scale ofthe display the display can be re-scaled to improve the visibility ofthe relative locations and orientations of the instrument and thetarget.

In step 3210 if the net distance greater than 90-percent of the maximumscale of the display an exception condition may exist and exceptionprocessing may be required.

In step 3212 the computer software rescales the real-time display toassure effective visibility of the movement and changes in orientationof the motion and orientation sensing module or device whenever the netdistance is less than 5-percent or greater than 50-percent of the scaleof the display.

In step 3214 whenever the distance is greater than 90-percent of themaximum scale of the display or an exception condition is detected,control is passed to the Exception Processing routine 3500.

In step 3216 the computer displays the trajectory of the motion andorientation of the active end of the instrument with respect to thetarget location and orientation for each of the first 100 data points.

In step 3218 the tracking software running on the computer checks if 100data samples have been processed. If equal to or greater than 100 datapoints the computer returns control to the top level of the trackingsoftware at step 2614.

FIG. 14 illustrates a simplified example flow chart of the stepsperformed by each motion and orientation sensing module or device inconjunction with the computer to analyze each additional movement andchange in orientation beyond the first 100 tracking data samples of aninstrument, probe, instrument, or equivalent equipment.

In step 3300 control is transferred to the software routine thatperforms the necessary actions to collect and display all remaining datapoints defining the movement, location, and orientation of an exampleprobe, tool, instrument, or alignment jigs or cutting blocks, or similarapparatus with respect to the target location and orientation in realtime.

In step 3302 the motion and orientation sensing module or devicecontinues to sample the dynamic acceleration data every 10 millisecondsthroughout the tracking procedure and transmits the data to thetelemetry receiver connected to the computer. If a second, or marker,example motion and orientation sensing device is positioned to track anychange in location or orientation of the target, the orientation anddynamic acceleration data from that device is also sampled every 10milliseconds. The data from the tracking device is adjusted by the datafrom the marker device to account for any changes in the orientation andlocation of the target. The adjusted data is transmitted to thetelemetry receiver connected to the computer.

In step 3304 the orientation and dynamic acceleration data for all threeCartesian axes with respect to the zenith and tangents to the surface ofthe earth from all three accelerometers is analyzed by the computer forreal-time display. The adjusted data is stored in the orientation andacceleration data arrays.

In step 3306 the data defining the net average velocity along eachCartesian axis is calculated for the duration of each sample intervaland stored in the velocity data array.

In step 3308 the data defining the net change in distance traveled alongeach Cartesian axis during each sample interval is calculated and storedin the location data array.

In step 3312 control is passed to the Display Tracking Data routine3400.

In step 3314 when control returns from the Display Tracking Date routine3400, the software examines the telemetry data to determine if a STOPcommand has been received, an exception condition detected, or the timewithout receiving data from the telemetry receiver has been exceeded.

In step 3316 whenever an exception condition is detected, a timeoutcondition occurs, or the STOP command is received, control is passed tothe Exception Processing routine 3500. If no exception condition or Stopcommand is detected, control is transferred to step 3312 and datacollection operations are continued.

FIG. 15 illustrates a simplified example flow chart of the stepsperformed by a computer to display each additional movement and changein orientation of an example embodiment of the motion and orientationsensing module or device. If a second, or marker, example motion andorientation sensing device is positioned to track any change in locationor orientation of the target, the tracking data can be adjusted toaccount for any movement or change in orientation of the target.

In step 3400 control is transferred to the software routine thatperforms the necessary actions to display all remaining data pointsdefining the movement, location, and orientation of an example probe,tool, instrument, or alignment jigs or cutting blocks, or similarapparatus.

In step 3402 the computer calculates and stores the average velocity,and net direction of movement between each pair of data points in thevelocity array.

In step 3404 the computer calculates and stores the net distancetraveled between each pair of data points in the location array.

In step 3406 if the net distance less than 5-percent of the scale of thedisplay the display is rescaled to improve the visibility of therelative locations and orientations of the instrument and the target.

In step 3408 if the net distance greater than 50-percent of the scale ofthe display the display is rescaled to improve the visibility of therelative locations and orientations of the instrument and the target.

In step 3410 if the net distance greater than 90-percent of the maximumscale of the display an exception condition may exist and exceptionprocessing may be required.

In step 3412 the computer software rescales the real-time display toassure effective visibility of the movement and changes in orientationof the motion and orientation sensing module or device whenever the netdistance is less than 5-percent or greater than 50-percent of the scaleof the display.

In step 3414 whenever the distance is greater than 90-percent of themaximum scale of the display or an exception condition is detected,control is passed to the Exception Processing 3500 routine.

In step 3416 the distance and differences in orientation of theinstrument with respect to the target location and orientation isplotted on the display screen in real time.

In step 3418 the computer returns control to Continue Collecting andDisplaying Movement and Orientation Tracking Data at step 3312.

FIG. 16 is a simplified example flow chart of the steps performed by acomputer to process exception conditions and automatically trigger theshutdown procedure if that becomes necessary to protect the integrity ofthe tracking procedure while maintaining data integrity. A simplifiedexample flow chart is illustrated of the steps performed by a computerto process time-outs, exception conditions, or STOP commands. Thisroutine maintains the integrity of the data while completing the captureand storage of unprocessed tracking data if it is valid. The trackingsoftware is shut down if that becomes necessary to assure the integrityof the tracking procedure.

In step 3500 control is transferred to the software routine thatperforms the necessary actions to process exception conditions, restartthe tracking procedure, or perform an orderly shutdown of the trackingprocedure depending on codes included in the call to this routine.

In step 3502 execution of other software routines is suspended whileexception processing is performed.

In step 3504 the computer checks for the presence of any error codes.

In step 3506 if an error code is active, the computer sounds an alertand displays the error code or codes on the display screen.

In step 3508 the computer places a question on the display screen askingthe user if the current tracking procedure is to be terminated.

In step 3510 if the answer is ‘no’ control will be returned to thecalling routine.

In step 3512 control is returned to the calling routine so collection,processing, and display of the distance and difference in orientationbetween the tracking motion and orientation sensing module or device andthe target can continue.

In step 3514 if the answer is not ‘no’ or there is no answer, thecomputer displays a request for, and records, audio, graphic,annotations, notes, attachments, and other inputs the user wantsappended to the data records of the current tracking procedure.

In step 3516 the computer places a question on the display screen askingthe user if the current tracking data is approved to be added to therecord of the current tracking procedure.

In step 3518 if the user approves the current tracking data, allassociated data records, audio files, graphic files, annotations, notes,attachments, and other inputs are stored within the record of thecurrent tracking procedure as the first step in the shutdown procedure.

In step 3520 the shutdown procedure continues and the computer ceases toupdate the display.

In step 3522 the user is reminded to turn off each motion andorientation sensing module or device.

In step 3524 execution of the motion and Orientation Tracking SoftwareProgram 2600 is terminated and the shutdown procedure is complete.

In step 3526 if the current tracking data is not approved, all currentdata records are deleted.

In step 3528 the computer places a question on the display screen askingthe user if the current tracking procedure is to be restarted. If not,Execution of the motion and Orientation Tracking Software Program 2600is terminated without saving any of the tracking data or any otherrecords.

In step 3530 if the user directs the software to restart the trackingprocedure, control is transferred to the routine for Prepare Motion andOrientation Sensing operation 2700 and the tracking process isre-started.

FIG. 17 is a simplified example of an initial computer display screenthat may be used to guide the movement and orientation of an instrumenthaving an example embodiment of a motion and orientation sensing moduleor device. FIG. 17 illustrates 3600 a simplified example of an initialimage on a computer display screen 2016 that may be used to guide themovement and orientation of an instrument having an example embodimentof the motion and orientation sensing module or device. With thereception of the initial telemetry data packet computer 2014, havingcomputer keyboard 2010 and computer mouse 2012, defines the initialposition of the active end of the example medical instrument as thetarget location. The target orientation is equal to the initial tilt andyaw of the instrument with respect to all three Cartesian axes alignedwith the zenith and tangents to the surface of the earth. Therepresentation of the physical location and orientation and targetlocation and orientation is displayed on computer display screen 2016.The target position and alignment image consists of an outer ring of abulls-eye image 3610, with radius A representing the scale of thebulls-eye in millimeters, an inner ring of the bulls-eye image 3614, andcrosshairs 3612 within the bulls-eye image 3610 on computer displayscreen 2016. The initial representation of the active end of theinstrument have an example motion and orientation sensing module ordevice is an image of a virtual circumference 3616 centered within theinner ring 3614 of the bulls-eye and likewise the Image of virtualcrosshairs 3618 coinciding with the central portion of the image of thecrosshairs 3612 of the target bulls-eye.

FIG. 18 is a simplified example of a computer display screenillustrating the position and location of an instrument having anexample embodiment of a motion and orientation sensing module or deviceas it is starting to approach the pre-defined target location andorientation. FIG. 18 illustrates 3700 a simplified example of a trackingimage on a computer display illustrating the position and orientation ofan instrument having an example embodiment of the motion and orientationsensing module or device attached, affixed, embedded, or integratedwithin it. The computer 2014, having computer keyboard 2010 and computermouse 2012, presents images on display 2016 representing theorientation, movement, and location of an example instrument withrespect to the target location and orientation. The target position andalignment image consists of an outer ring of a bulls-eye image 3610,with radius B representing the scale of the bulls-eye in decimeters, aninner ring of the bulls-eye image 3614, and crosshairs 3612 within thebulls-eye image 3610 on computer display screen 2016. In this figure theinstrument is positioned at a distance from the physical target.Computer display 2016 is updated in real time whenever the user movesthe example instrument. To assure alignment in all three dimensions, theimage of the example instrument is represented as a cylinder 3722 withcrosshairs 3618 circumferences 3616, 3720 at both ends. The degree ofalignment of both circumferences 3616, 3720 of the ends of cylinder 3722represent orientation in the third dimension and may be easier tocorrelate with physical space than the usual two dimensionalrepresentation of three dimension graphs. This example representationalof three dimensional spaces may be readily presented on 3 D displays.

The heading of a motion and orientation sensing module or device ismeasured and tracked by two tri-axial accelerometers positioned at thelongitudinal ends of an example motion and orientation sensing module ordevice. The tilt of the forward tri-axial accelerometer with respect tothe orientation of the physical target is represented by the orientationof the image of the virtual crosshairs 3618 with respect to targetcrosshairs 3612 on display screen 2016. The second integral of thealgebraic sum of the acceleration in all a three Cartesian axes of theforward tri-axial accelerometer determines the distance between theactive edge of the example instrument and the target. The differencesbetween the calculated locations of each end of the example motion andorientation sensing module or device along its longitudinal axis definesits relative heading, or the yaw required to align longitudinal axis ofthe example motion and orientation sensing module or device in the X, Yplane. The estimate of the difference in location determines therelative size and location of the image 3616, 3618, 3720, 3722 of theinstrument with respect to the image of the inner circle of the targetlocation 3614.

As the example instrument approaches the target location themagnification of the display may be automatically increased tofacilitate more precise movement and orientation of the exampleinstrument as it gets closer to the target location.

FIG. 19 is a simplified example of a computer display screenillustrating changes in the display as an instrument having an exampleembodiment of a motion and orientation sensing module or device is movedtowards the target location and orientation. FIG. 19 illustrates 3800 asimplified example of a computer display 2016 illustrating the movementof an instrument having an example embodiment of the motion andorientation sensing module or device attached, affixed, embedded, orintegrated within it as it moves towards a physical target. Computer2014, having computer keyboard 2010 and computer mouse 2012, processesall orientation and movement data with respect to the initial locationand orientation of the example instrument. Computer display 2016 isupdated in real time whenever the user moves the example instrument withrespect to the target orientation and orientation. The target positionand alignment image consists of an outer ring of a bulls-eye image 3610,with radius C representing the scale of the bulls-eye in centimeters, aninner ring of the bulls-eye image 3614, and crosshairs 3612 within thebulls-eye image 3610 on computer display screen 2016. This movement isillustrated as multiple images of virtual cylinders on computer display2016. The three cylinders 3820, 3822, 3824 illustrated in this figurerepresent the same physical device with each image representing itslocation and orientation as it is moved towards the target location andorientation.

The target location and orientation is represented by the image of abulls-eye with crosshairs 3612 and circles 3610, 3614. To assurealignment in all three dimensions, the representation of the exampleinstrument is represented by images of virtual cylinders 3820, 3822, and3824 with images of virtual crosshairs 3826, 3828, and 3830. The degreeof alignment of the virtual crosshairs 3826, 3828, 3830 with bulls-eyecrosshairs 3612 illustrates the relative orientation of the instrumentbeing tracked in two axes. The degree of alignment of the ends of theimages of each of the virtual cylinders 3820, 3822, 3824 represents therelative orientation in the third dimension. The degree of alignment andrelative size of the circumferences of virtual cylinders 3820, 3822, and3824 with the inner bulls-eye ring 3614 illustrates the relativelocation of the instrument being tracked with respect to the target.

As the example instrument approaches the target location themagnification of the display may continue to automatically increase tofacilitate more precise movement and orientation of the exampleinstrument as it gets closer to the target location.

FIG. 20 is a simplified example of a computer display screenillustrating changes in the display as an instrument having an exampleembodiment of a motion and orientation sensing module or deviceapproaches the target location and orientation. FIG. 20 illustrates 3900a simplified example of a computer display 2016 illustrating themovement of an instrument having an example embodiment of the motion andorientation sensing module or device attached, affixed, embedded, orintegrated within it as it moves towards a physical target. Computerdisplay 2016 is updated whenever the user moves the example instrumentwith respect to the target orientation and orientation. Computer 2014,having computer keyboard 2010 and computer mouse 2012, processes allorientation and movement data with respect to the initial location andorientation of the example instrument and updates computer display 2016in real time as the motion and orientation sensing module or device ismoved. The target position and alignment image consists of an outer ringof a bulls-eye image 3610, with radius A representing the scale of thebulls-eye in millimeters, an inner ring of the bulls-eye image 3614, andcrosshairs 3612 within the bulls-eye image 3610 on computer displayscreen 2016.

The three virtual circumferences 3926, 3930, 3934, with images ofvirtual crosshairs 3936, 3938, 3940 in this figure represent the samephysical device with each image representing its location andorientation as it is moved towards the target location and orientation.This movement is illustrated by separating these multiple imagesrepresenting the instrument being tracked by arrows 3928, and 3932. Thetarget location and orientation is represented by the image of abulls-eye with crosshairs 3612 and circles 3610, 3614. The degree ofalignment of the virtual circumferences 3926, 3930, 3934 with the innerbulls-eye ring 3614 illustrates the relative location of the instrumentbeing tracked with respect to the target. The degree of alignment of thevirtual crosshairs 3936, 3938, 3940 with bulls-eye crosshairs 3612illustrates the relative orientation of the instrument being trackedwith respect to the target.

As the example instrument approaches the target location themagnification of the display may continue to automatically increase tofacilitate more precise movement and orientation of the exampleinstrument as it gets closer to the target location.

FIG. 21 is a simplified example of a computer display screenillustrating the final position and orientation of an instrument havingan example embodiment of a motion and orientation sensing module ordevice precisely aligned with the target location and orientation. FIG.21 illustrates 4000 a simplified example of a computer display 2016illustrating the location and orientation of an instrument having anexample embodiment of the motion and orientation sensing module ordevice attached, affixed, embedded, or integrated within it when itarrives at the target location and is aligned with the targetorientation. The target position and alignment image consists of anouter ring of a bulls-eye image 3610, with radius A representing thescale of the bulls-eye in millimeters, an inner ring of the bulls-eyeimage 3614, and crosshairs 3612 within the bulls-eye image 3610 oncomputer display screen 2016. Computer 2014, having computer keyboard2010 and computer mouse 2012, processes all orientation and movementdata with respect to the initial location and orientation of the exampleinstrument. In this figure the example instrument is in contact with thephysical target, even if the target itself is not visible to thephysician. Concentric circles 4014, 4016, representing the virtualcircumferences of the longitudinal axis of the example instrument, arecentered on a third circle 3614 representing the inner bulls-eye ring ofthe image of the target location. Virtual crosshairs 4012, representingthe orientation of the cross-section of the longitudinal axis of theexample instrument, are coincident with crosshairs 3612 representing theorientation of the target location. The combination of these threeconcentric circles along with the alignment of the crosshairs indicatesthat the example medical instrument is positioned precisely at thetarget location and aligned precisely with the target orientation in allthree Cartesian coordinates aligned with the zenith and tangents to thesurface of the earth.

FIG. 22 is a simplified perspective cut-away view of an example motionand orientation sensing module or device. FIG. 22 illustrates 4100 asimplified perspective cut-away view of an example motion andorientation sensing module or device enclosed in encapsulating shell.Enclosure 4108 may be either hermetic or non-hermetic depending on theapplication. Substrate 4134 provides mechanical support for the internalcomponents of the motion and orientation sensing module or device, aswell as electrical interconnect for the electronic circuitry. POWERswitch 4124 is used to turn the motion and orientation sensing module ordevice on and off. START switch 4126 is used to initiate the trackingprocedure or restart it if it has been interrupted. STOP switch 4128 isused to pause or terminate the tracking procedure. Battery 4132, or anequivalent energy storage device, provides power for the operation ofthe electronic circuitry and telemetry transmissions by telemetrytransmitter or transceiver 4122 through antenna 4120. Passive components4102 support the integrated circuits to implement the full electricalschematic. The electrical Non-volatile memory 4136 stores theidentification code of the motion and orientation sensing module ordevice as well as calibration constants, battery voltage, temperature,and other programmable data. Tri-axial accelerometer 4104 detectsmovement in all three Cartesian axes and tilt with respect to the zenithand tangents to the surface of the earth. It is positioned at one end ofthe longitudinal axis of the motion and orientation sensing module ordevice, and tracks the distance between the leading or active edge of amedical instrument and the target. Accelerometer 4104 also tracks theorientation of the cross section of the motion and orientation sensingmodule or device. MUX/DEMUX 4110 interfaces between the individualsensing elements within the accelerometers to enable their analogoutputs to be processed by analog to digital conversion (ADC) circuitry4112. Hi-pass filter 4114 provides inputs to event detection circuitry.Low-pass filter 4116 limits the bandwidth of analog signals coupled tothe analog to digital conversion circuitry 4112 to reduce electricalnoise and out-of-band signals. Tri-axial accelerometer 4118 detectsmovement in all three Cartesian axes and tilt with respect the zenithand tangents to the surface of the earth. It is positioned at theopposite end of the longitudinal axis of the motion and orientationsensing module or device from triaxial accelerometer 4104. Accelerometer4118 tracks the distance between the trailing edge of an example medicalinstrument and the target. Micro control unit 4106 controls theoperation of the motion and orientation sensing module or device as wellas data processing functions performed within it.

Motion and orientation sensing modules and devices having dualaccelerometers are not only capable of providing more accurate yaw data,but have an inherent level of redundancy that aids in the confirmationthat the instrument is guided accurately to the target position andorientation. This combination of electrical, mechanical, and RFcomponents enables the construction of extremely small, high resolution,low-power, hermetic, wireless motion and orientation sensing devices.

FIG. 23 is a simplified block diagram 4200 of an example informationtechnology system and components integrating the data captured by amotion and orientation sensing module or device and displaying itsprogress in real time. This network of devices enables the real-timeacquisition and sharing of information to enable more effective decisionmaking as well as collective understanding of medical histories andconditions. The motion and orientation sensing module or device 2006includes a telemetry transmitter or transceiver. This transmits data4212A to telemetry receiver 4210 networked or connected 4210A tocomputer system 4208. Computer system 4208 is also connected online4208A to internet cloud services 4214. This enables data to be storedwithin cloud services 4214 within the internet or within dedicatedelectronic health record databases 4202 that are connected 4202A to theinternet. It also facilitates accessing data through other computers andother information devices such as smartphones 4204 that are wirelesslyconnected 4204A to the internet and tablets 4206 that are also connectedwirelessly 4206A to the internet. This network and collection ofservices and data peripherals enable patient data to be shared worldwideamong appropriate physicians and healthcare facilities as needed toassure patient care and safety.

FIG. 24 illustrates a simplified block diagram 4300 of the basicconstruction of a generic accelerometer. The general sensing structureof most accelerometers is a proof mass 4306 that is restrained by someform of resistive mechanical supports 4302 such as springs or flexiblesupports having anchor points 4304. The proof mass 4306 and resilientmechanical supports 4302 may be fabricated with micromachining processesin combination with standard integrated circuit fabrication processes.At rest or under constant velocity the electrical sensing element 4310maintains a constant level of capacitance, resistance, charge, voltage,or current. Electrical signals output by electrical sensing element 4310may be converted into digital signals by additional circuitry integratedwithin the accelerometer integrated circuit or connected to it. Thisdigital data may be used to track, analyze, store, and display themovement and changes in orientation of an accelerometer.

FIG. 25 illustrates a simplified block diagram 4400 of the basicconstruction of a generic accelerometer subjected to acceleration vector4408. The acceleration may be constant, such as acceleration due to theforce of gravity, or variable. The general sensing structure of mostaccelerometers is a proof mass 4306 that is restrained by some form ofresistive mechanical supports 4302 such as springs or elastic supportshaving anchor points 4304. The proof mass 4306 and resilient mechanicalsupports 4302 may be fabricated with micromachining processes incombination with standard integrated circuit fabrication processes.Vectors of acceleration 4408 normal to the support axis cause the proofmass 4306 to move relative to the anchor points 4304. The movement ofthe proof mass 4306 displaces portions of electrical sensing element4310 changing its electrical parameters or outputs. These parameters mayinclude capacitance or resistance, or the output of charge, voltage, orcurrent. The acceleration due to gravity may also hold the proof mass4306 in a position that is electrically detectable. This enables thedetection of tilt with respect to the earth's surface. Electricalsignals output by electrical sensing element 4310 may be converted intodigital signals by additional circuitry integrated within theaccelerometer integrated circuit or connected to it. This digital datamay be used to track the movement and changes in orientation of theaccelerometer.

FIG. 26 illustrates a simplified block diagram 4500 of the orientationof generic accelerometers within a tri-axial accelerometer die, chip,integrated circuit, hybrid circuit, or electronic module. Most MEMSaccelerometers operate in-plane, that is, they are designed to besensitive only to a direction in the plane of the die. By integratingtwo devices 4504, 4508 at right angles on a single die a two-axisaccelerometer can be fabricated. By adding an additional out-of-planedevice 4506 all three Cartesian axes can be detected and quantized witha single triaxial accelerometer device. The out-of-plane device 4506 maybe fabricated with additional MEMS processes integrating all threeaccelerometers within the same integrated circuit die or chip. Onedeterminate of the accuracy of a tri-axial accelerometer is theprecision of the relative orientation of each of the three accelerationsensing elements. Integration of all three acceleration sensing elementson a single die or chip may result in lower misalignment error thanthree discrete accelerometers combined within a single package ormounted directly onto a silicon die or chip, PWB, or other substrate4502.

FIG. 27 illustrates a simplified schematic block diagram 4600 of anexample motion and orientation sensing module or device having twotri-axial capacitive accelerometers. Capacitive accelerometersfabricated on integrated circuit die are primarily bulk MEMS structures.Capacitive accelerometers have a moveable micromachined feature thatacts as one side of a variable capacitor with respect to a fixedstructure within the integrated circuit die. Movement of the integratedcircuit causes displacement of this moveable structure resulting in achange in the level of capacitance. The change in capacitance produces achange in output frequency or analog voltage that is proportional to thesum of dynamic and static acceleration. Capacitive accelerometers areDC-responding with high sensitivities, narrow bandwidth, and outstandingtemperature stability. These devices are well suited for measuringlow-frequency vibration, motion, and steady-state acceleration such asgravity.

Two accelerometers 4602, 4604 are positioned at each end of thelongitudinal axis of the motion and orientation sensing module ordevice. The forward tri-axial accelerometer 4604 tracks the movement ofthe leading edge or active face of an example instrument. Thisaccelerometer 4604 also tracks the orientation of the cross section ofthe motion and orientation sensing module or device. The trailingaccelerometer 4602 tracks the orientation of the longitudinal axis ofthe motion and orientation module or device. The combination of the twotri-axial accelerometers 4602, 4604 can be used to measure heading andyaw in the X-Y plane with high accuracy. The sensing elements withincapacitive tri-axial accelerometers 4602, 4604 generate analogelectrical signals whenever the motion and orientation sensing module ordevice is moved or rotated. These analog signals also have a DCcomponent depending on their orientation with respect to the nadir. Theeffective number of bits of a capacitive, or a variable capacitance,accelerometer depends on the resolution of changes in capacitanceresulting from displacement of the plates of the sensing capacitorswithin the accelerometer. The combination of the two accelerometers4602, 4604 assures the motion and orientation sensing module or devicecan be guided precisely to the target location and orientation in allthree Cartesian axes with no discrepancies in pitch, roll, or yaw.

Motion and orientation sensing modules and devices having twoaccelerometers are not only capable of providing more accurate yaw data,but two accelerometers also provide a level of redundancy that aids inthe confirmation that an instrument is guided accurately to the targetposition and orientation. If data generated by the two accelerometers4602, 4604 contain a discrepancy, the tracking procedure may have beencompromised and the user can be alerted to the possibility of anexception condition that needs to be addressed.

Multiplexor (MUX) 4606 interfaces the acceleration sensing elements ofaccelerometers 4602, 4604 with the input of capacitance to voltageconvertor 4608. The analog signals output by the capacitance to voltageconversion circuitry 4608 drive the input of the analog to digitalconversion circuitry (ADC) 4112. The digital values output by ADC 4112are transmitted by telemetry transceiver or transmitter 4122 throughantenna 4120. This enables an external computer system or otherinformation technology appliance to receive the radio frequency signalbroadcast by the motion and orientation sensing module or device forsubsequent processing, storage, and display in real time.

Control logic and calibration circuitry 4616 controls the operation ofthe electronic components within an example motion and orientationsensing module or device as well as additional data processing requiredbefore transmitting data to a computer system. Battery 4132, or anequivalent energy storage device, provides the power to operate theelectronic circuitry within the motion and orientation sensing module ordevice. Substrate 4620 provides mechanical support and electricalinterconnect for the electronic components and battery within theexample motion and orientation sensing module or device.

The illustrated components and interconnect will enable tracking themovement and orientation of a medical probe, tool, instrument, alignmentjig, cutting block, or similar equipment having a motion and orientationsensing module or device, accurately with a high level of precision.

FIG. 28 illustrates a simplified schematic block diagram 4700 of anexample motion and orientation sensing module or device having twotri-axial piezoresistive or piezoelectric accelerometers. Piezoresistiveaccelerometers fabricated on integrated circuit die are primarily bulkMEMS structures. Piezoresistive accelerometers have a beam ormicromachined feature whose resistance changes as it is flexed bymovement of the proof mass. The change in resistance produced by flexingthe cantilever produces a change in resistance that is proportional tothe sum of dynamic and static acceleration. The effective number of bitsof a piezoresistive accelerometer depends on the resolution of changesin resistance as acceleration flexes the cantilever within theaccelerometer. Piezoresistive accelerometers are DC-responding with highsensitivities, narrow bandwidth, and outstanding temperature stability.These devices are well suited for measuring low-frequency vibration,motion, and steady-state acceleration.

The two accelerometers 4702, 4704 are positioned at each end of thelongitudinal axis of an example motion and orientation sensing module ordevice. The forward tri-axial accelerometer 4704 tracks the movement ofthe leading edge or active face of the example instrument. Thisaccelerometer 4704 also tracks the orientation of the cross section ofthe motion and orientation sensing module or device. The trailingaccelerometer 4702 tracks the orientation of the longitudinal axis ofthe example motion and orientation module or device. The combination ofthe two tri-axial accelerometers 4702, 4704 can be used to measureheading and yaw in the X-Y plane with high accuracy. The sensingelements within piezoresistive tri-axial accelerometers 4702, 4704generate analog electrical signals whenever the example motion andorientation sensing module or device is moved or rotated. These analogsignals also have a DC component depending on their orientation withrespect to the nadir. The combination of the two accelerometers 4702,4704 assures the motion and orientation sensing module or device can beguided precisely to the target location and orientation in all threeCartesian axes with no discrepancies in pitch, roll, or yaw.

Motion and orientation sensing modules and devices having twoaccelerometers are not only capable of providing more accurate yaw data,but also two accelerometers provide a level of redundancy that aids inthe confirmation that the example instrument is guided accurately to thetarget position and orientation. If data generated by the twoaccelerometers 4702, 4704 contain a discrepancy, the tracking proceduremay have been compromised and the user can be alerted to the possibilityof an exception condition that needs to be addressed.

Multiplexor (MUX) 4606 interfaces the acceleration sensing elements ofaccelerometers 4702, 4704 with the input to analog conversion circuitry(ADC) 4112. The digital values output by ADC 4112 are transmitted bytelemetry transceiver or transmitter 4122 through antenna 4120. Thisenables an external computer system or other information technologyappliance to receive the radio frequency signal broadcast by the motionand orientation sensing module or device for subsequent processing,storage, and display in real time.

Control logic and calibration circuitry 4716 controls the operation ofthe electronic components within the motion and orientation sensingmodule or device as well as additional data processing that may berequired before transmitting the data to a computer system. Battery4132, or an equivalent energy storage device, provides the power tooperate the electronic circuitry within the motion and orientationsensing module or device. Substrate 4720 provides mechanical support andelectrical interconnect for the electronic components and battery withinthe motion and orientation sensing module or device. The illustratedcomponents and interconnections will enable tracking the movement andorientation of a medical probe, tool, instrument, alignment jig, cuttingblock, or similar equipment having a motion and orientation sensingmodule or device, accurately with a high level of precision.

FIG. 29 illustrates a simplified schematic block diagram 4800 of anexample motion and orientation sensing module or device having tri-axialforce-balanced or force feedback capacitance bridge accelerometers. Thesensing elements within capacitive tri-axial force-balancedaccelerometers generate analog electrical signals whenever an examplemotion and orientation sensing module or device is moved or rotated aswell as a constant output component depending on each accelerometer'sorientation with respect to the nadir. In a force-balanced capacitiveaccelerometer the signal generated by changes in capacitance isamplified and fed back to the sensing structure to counteract thedisplacement of the moveable capacitor plates. This negative feedbacksignal is also routed to input of the analog to digital converter.Because the output is dependent only on the feedback force, anddisplacements of the moveable capacitor plates are minimized, minimizingnonlinearities from the mechanical system and the electronics interfaceas well. The change in the feedback voltage is proportional to the sumof dynamic and static acceleration. This feedback voltage is output tothe analog to digital circuitry for transmission to a computer systemhaving a real-time display. Force-balance capacitive accelerometers areDC-responding with very high sensitivities, narrow bandwidth, andoutstanding temperature stability. These devices are well suited formeasuring low-frequency vibration, motion, and steady-state accelerationsuch as gravity.

The effective number of bits of a force-balanced capacitor bridgeaccelerometer depends on the resolution of changes in capacitance causedby acceleration displacing the moveable plates of the capacitor bridgewithin the accelerometer. In many instances reduction in nonlinearitiesand noise improves the effective number of bits achieved withforce-balanced capacitor bridge accelerometers.

The two accelerometers 4802, 4804 are positioned at each end of thelongitudinal axis of the motion and orientation sensing module ordevice. The forward tri-axial accelerometer 4804 tracks the movement ofthe leading edge or active face of a medical instrument. Thisaccelerometer 4804 also tracks the orientation of the cross section ofthe example motion and orientation sensing module or device. Thetrailing accelerometer 4802 tracks the orientation of the longitudinalaxis of the motion and orientation module or device. The combination ofthe two tri-axial accelerometers 4802, 4804 can be used to measureheading and yaw in the X-Y plane with high accuracy and assure themotion and orientation sensing module or device can be guided preciselyto the target location and orientation in all three Cartesian axes withno discrepancies in pitch, roll, or yaw.

Motion and orientation sensing modules and devices having twoaccelerometers are not only capable of providing more accurate yaw data,but also two accelerometers provide a level of redundancy that aids inthe confirmation that the example instrument is guided accurately to thetarget position and orientation. If data generated by the twoaccelerometers 4802, 4804 contain a discrepancy, the tracking proceduremay have been compromised and the user can be alerted to the possibilityof an exception condition that needs to be addressed.

Multiplexor (MUX) 4606 interfaces the acceleration sensing elements withthe input of charge amplifier and filter 4832. The analog signals outputby charge amplifier and filter 4832 drive the input of sigma-deltamodulator 4834. The signals output by sigma-delta modulator 4834 drivethe input of analog to digital conversion circuitry (ADC) 4112. Thebinary values output by ADC 4112 are transmitted by telemetrytransceiver or transmitter 4122 through antenna 4120. This enables anexternal computer system or other information technology appliance toreceive the radio frequency signal broadcast by the motion andorientation sensing module or device for subsequent processing, storage,and display.

The output of sigma-delta modulator 4834 also drives comparator 4822.Comparator 4822 drives control logic and latch 4824. The outputs ofcontrol logic and latch 4824 drive the top control 4826 and bottomcontrol 4828 circuits of the feedback loop of the force balanced sensingelements with tri-axial accelerometers 4802, 4804. These controls areconnected, through de-multiplexor 4830, to fixed structures withintri-axial accelerometers 4802, 4804. The outputs of the top and bottomcontrols 4826, 4828 act through fixed structures within tri-axialaccelerometers 4802, 4804 to re-center the proof masses that aredisplaced by movement or tilt of the motion and orientation sensingmodule or device. Tri-axial accelerometers 4802, 4804 continue to outputanalog signals through MUX 4606 to charge amplifier 4832 and sigma-deltamodulator 4834 until each of the proof masses have been pulled back totheir center position. The electrical signal that is required to offsetdisplacement of each proof mass is also the analog input to ADC 4112.

Control logic and calibration circuitry 4816 controls the operation ofthe electronic components within the example motion and orientationsensing module or device as well as additional data processing that maybe required before transmitting the data to a computer system. Battery4132, or equivalent energy storage device, provides the power to operatethe electronic circuitry within the example motion and orientationsensing module or device. Substrate 4820 provides mechanical support andelectrical interconnect for the electronic components and battery withinthe motion and orientation sensing module or device. The illustratedcomponents and interconnection will enable tracking the movement andorientation of a medical probe, tool, instrument, alignment jig, cuttingblock, or similar equipment having a motion and orientation sensingmodule or device, accurately with a very high level of precision.

FIG. 30 illustrates a simplified schematic block diagram 4900 of a basicgeneric accelerometer with the associated circuitry needed toincorporate dithering, oversampling, and decimation functions to improvethe signal to noise ration and the effective number of bits. Thesefunctions can be combined to extend the effective number of bits ofaccelerometer 4102 by three or more least-significant-bits.Over-sampling the analog signal from the sensing element ofaccelerometer 4102 with analog to digital converter 4906 increases thenumber of discrete samples compromising the digitization of the analogwaveform. Low pass anti-aliasing filter 4904 removes the aliases,harmonics, intermodulation products, and other out-of-band signals andreduces the noise passed on to the analog to digital converter 4906.Quantization filter 4910 can reduce quantization noise without reducingthe binary output of the ADC 4906. Decimator 4912 digitally down-samplesthe stream of over-sampled, dithered 4908, digital values. Thecombination of these functions extends the effective number of bits ofthe data conversion chain linking physical acceleration to a digitizedwaveform.

The likelihood of an analog signal being exactly equal to a digitalvalue is small. Therefore, with the combination of dithering andoversampling, it is possible to develop an accurate estimate of theactual value of a point on an analog waveform to greater levels ofresolution than the least significant bit of the analog to digitalconverter 4906. The intermediate result is the creation of more digitalreadings than specified by the Nyquist frequency. Anti-alias filtering4904 can be applied before sampling the analog waveform. Only pure sinewaveforms are harmonic free. Even then, non-linarites may createharmonics and intermodulation products. Therefore anti-aliasing mustremove these harmonic signals and intermodulation products because theyintroduce nonrandom distortions into the oversampling of dithered analogwaveforms. Low-pass anti-aliasing filter 4904 also eliminates otherfrequencies above the Nyquist frequency before the analog signal isover-sampled. To minimize the risk of higher frequency artifacts fallinginto the oversampled pass-band and reducing the signal-to-noise ratio.

Dithering 4908 the analog input signal adds a noise component to thesignal on the order of a least significant bit or more. Adding thiswhite or Gaussian noise component creates a stochastic variable with amean value of zero for each voltage sample from the analog waveform. Thecombination of dithering 4908 and oversampling 4906 enables theinterpolation of analog values at each point on the analog waveform. Foreach desired additional bit of resolution the analog signal can beoversampled by four times. Over sampling by this amount halves thequantization noise introduced by the quantization steps. This canincrease the resolution of the measurement by one-half bit.

The greater the samples rate of the analog to digital conversioncircuitry the better the representation of the input signal, whensamples are subsequently combined. This sample rate may be as little astwice the Nyquist frequency to as much as 256 times the Nyquistfrequency, filtering with quantization noise filter 4910 anddown-sampling these over-sampled digital values with decimator 4912increases the signal-to-noise ratio of the analog to digital conversionprocess. Decimation 4912 down-samples the over-sampled digital values byaggregating groups of over-sampled digital values with the number ofdigital values within each group depending on the down-sampling divisor.Each down-sampled digital value is right shifted to scale the answercorrectly for the increased level of resolution to develop the finalhigh-resolution digital output. The illustrated components andinterconnect can enable improvement of the resolution of the analog todigital conversion process, and therefore the least significant bit, byseveral bits.

FIG. 31 is a simplified schematic block diagram 5000 of an examplemotion and orientation sensing module or device having tri-axialforce-balanced, force feedback, servo mode capacitance bridgeaccelerometers, capacitive accelerometers incorporating filtering,dithering, oversampling, decimation, ratiometric, and temperaturesensing functions to improve the signal to noise ration and theeffective number of bits. The sensing elements within capacitivetri-axial force-balanced accelerometers generate analog electricalsignals whenever an example motion and orientation sensing module ordevice is moved or rotated as well as a constant output componentdepending on each accelerometer's orientation with respect to the nadir.In a force-balanced capacitive accelerometer the signal generated bychanges in capacitance is amplified and fed back to the sensingstructure to counteract the displacement of the moveable capacitorplates. This negative feedback signal is also routed to input of theanalog to digital to analog converter. Because the output is dependentonly on the feedback force, and displacements of the moveable capacitorplates are minimized, minimizing nonlinearities from the mechanicalsystem and the electronics interface as well. The change in the feedbackvoltage is proportional to the sum of dynamic and static acceleration.This feedback voltage is output to the analog to digital circuitry fortransmission to a computer system having a real-time display.Force-balance capacitive accelerometers are DC-responding with very highsensitivities, narrow bandwidth, and outstanding temperature stability.These devices are well suited for measuring low-frequency vibration,motion, and steady-state acceleration such as gravity.

The effective number of bits of a force-balanced capacitor bridgeaccelerometer depends on the resolution of the feedback voltage requiredto offset changes in capacitance caused by acceleration of the moveableplates of the capacitor bridge within the accelerometer. This feedbackvoltage is an analog value, and in continuously operatingaccelerometers, is a point on an analog waveform. The likelihood of ananalog signal being exactly equal to a digital value is small.Therefore, the analog to digital conversion circuitry outputs a digitalvalue either slightly higher or lower than the analog value. Thisdetermines the resolution, or least significant bit, of the conversionof acceleration, a continuous physical phenomenon, into a digital value,an electrical code. It is possible to develop a more accurate estimateof the actual value of a point on an analog waveform and achieve greaterlevels of resolution with the addition of anti-alias filtering,dithering, oversampling, filtering quantization noise, and decimatingthe filtered, over-sampled signal. This can improve least significantbit of the analog to digital conversion process by several bits.

The sigma-delta modulator is a key component of sigma-delta analog todigital conversion circuitry, but it may not be the same as thesigma-delta modulator used to drive the force-feedback loop in aforce-balanced capacitive bridge accelerometer. In practice some of thefunctions may be merged. But it is important to note that the effectiveresolution of a Delta-Sigma ADC is dependent on the sample rate. Thismay not be the same as the optimal sample rate for centering proofmasses with the force-feedback control loop.

The two accelerometers 4802, 4804 are positioned at each end of thelongitudinal axis of the example motion and orientation sensing moduleor device. The forward tri-axial accelerometer 4804 tracks the movementof the leading edge or active face of a medical instrument. Thisaccelerometer 4804 also tracks the orientation of the cross section ofthe example motion and orientation sensing module or device. Thetrailing accelerometer 4802 tracks the orientation of the longitudinalaxis of the motion and orientation module or device. The combination ofthe two tri-axial accelerometers 4802, 4804 can be used to measureheading and yaw in the X-Y plane with high accuracy and assure themotion and orientation sensing module or device can be guided preciselyto the target location and orientation in all three Cartesian axes andwith no discrepancies in pitch, roll, or yaw.

Motion and orientation sensing modules and devices having twoaccelerometers are not only capable of providing more accurate yaw data,but also two accelerometers provide a level of redundancy that aids inthe confirmation that the example instrument is guided accurately to thetarget position and orientation. If data generated by the twoaccelerometers 4802, 4804 contain a discrepancy, the tracking proceduremay have been compromised and the user can be alerted to the possibilityof an exception condition that needs to be addressed.

Multiplexor (MUX) 4606 interfaces the force feedback signals fromaccelerometers 4802, 4804 with the input of charge amplifier and filter4832. The analog signals output by charge amplifier and filter 4832drive the input of sigma-delta modulator 4834. The sigma-delta analog todigital converter 5040 over-samples the analog signal output by thesigma-delta modulator 4834 and filtered through anti-alias low-passfilter 4904. Low-pass anti-aliasing filter 4904 eliminates frequenciesabove the Nyquist frequency. Harmonics, intermodulation products, andother high frequency artifacts can be removed before oversampling theanalog waveform because they can introduce nonrandom distortions intothe oversampled, dithered analog waveforms. Dithering 4908 is introducedinto the filtered analog waveform and the analog signal is over-sampledby sigma-delta analog to digital converter 5040. The combination ofdithering 4908 and oversampling by the sigma-delta analog to digitalconverter 5040 enables the interpolation of analog values at each pointon the analog waveform. The digital values output by sigma-delta analogto digital conversion circuitry 5040 are filtered through quantizationfilter 4910 and input to decimator 4912. Filtering with quantizationnoise filter 4910 and down-sampling the over-sampled digital values withdecimator 4912 further increases the signal-to-noise ratio of the analogto digital conversion process. Decimator 4912 digitally down-samples thestream of over-sampled digital values, and in conjunction with dithering4908 and oversampling 5040, can extend the effective number of bits byseveral least significant bits. The output of decimator 4912 drives datapacketizer 5034. Data packetizer 5034 assembles data into theappropriately formatted packets for transmission by telemetrytransceiver or transmitter 4122. The telemetry broadcasts are radiatedby antenna 4120. This enables an external computer system or otherinformation technology appliance to receive the radio frequency signalbroadcast by the motion and orientation sensing module or device forsubsequent processing, storage, and display in real time.

The output of sigma-delta modulator 4834 also drives comparator 4822.Comparator 4822 determines the value of feedback voltage required toforce-balance the moveable capacitor plates within the capacitancebridge of the acceleration sensing structure with each of the tri-axialaccelerometers 4802, 4804. This is input to control logic and latch4824. The outputs of control logic and latch 4824 drives the top control4826 and bottom control 4828 circuits to drive the moveable capacitorplates within the capacitance bridge of the acceleration sensingstructure back to their center points. These control signals areconnected, through de-multiplexor 4830, to the feedback structureswithin tri-axial accelerometers 4802, 4804. The outputs of the top andbottom controls 4826, 4828 act through the feedback structures withintri-axial accelerometers 4802, 4804 to re-center proof masses that havebeen displaced by movement or changes in orientation of the motion andorientation sensing module or device. Tri-axial accelerometers 4802,4804 continue to output analog signals through MUX 4606 to chargeamplifier 4832 and sigma-delta modulator 4834 until each of the proofmasses have been returned to their center position. The electricalsignal that is required to offset displacement of each proof mass isalso the analog input to sigma-delta analog to digital converter 5040 asdescribed in the previous paragraphs.

Control logic and calibration circuitry 5046 controls the operation ofthe electronic components within the motion and orientation sensingmodule or device as well as additional data processing that may berequired before transmitting the data to a computer system. Data fromtemperature sensor 5048 is incorporated into the automatic calibrationroutine executed whenever a motion and orientation sensing module ordevice is powered up. The data gathered during the automatic calibrationroutine are stored in nonvolatile memory 4136 within the motion andorientation sensing module or device. Battery 4132, or equivalent energystorage device, provides the power to operate the electronic circuitrywithin the motion and orientation sensing module or device. Ratiometricdesign reduces sensitivity of the data capture and conversion circuitryto fluctuations in supply and reference voltages as well as noise onpower conductors. Precision voltage reference 5050 provides additionalprotection against variations in reference voltages. Substrate 5020provides mechanical support and electrical interconnect for theelectronic components and battery within the motion and orientationsensing module or device. The illustrated components and interconnectwill enable tracking the movement and orientation of a medical probe,tool, instrument, alignment jig, cutting block, or similar equipmenthaving a motion and orientation sensing module or device, accuratelywith a very high level of precision.

FIG. 32 is a simplified schematic block diagram 5100 of an examplemotion and orientation sensing module or device having tri-axialpiezoresistive accelerometers incorporating filtering, dithering,oversampling, decimation, ratiometric, temperature sensing, and eventdetection functions to improve the effective number of bits andrepeatability of data collection and processing. The sensing elementswithin piezoresistive tri-axial accelerometers generate analogelectrical signals whenever an example motion and orientation sensingmodule or device is moved or rotated as well as a constant outputcomponent depending on each accelerometer's orientation with respect tothe nadir. Piezoresistive accelerometers have a beam or micromachinedfeature whose resistance changes as it is flexed by movement of theproof mass. The change in resistance produced by flexing the cantileveris proportional to the sum of dynamic and static acceleration.Piezoresistive accelerometers are DC-responding with high sensitivities,narrow bandwidth, and outstanding temperature stability. These devicesare well suited for measuring low-frequency vibration, motion, andsteady-state acceleration such as gravity.

The effective number of bits of a piezoresistive accelerometer dependson the resolution of changes in resistance as acceleration flexes theresistive cantilever within the accelerometer. Changes in resistance areanalog values, and in continuously operating accelerometers, are pointson an analog waveform. The likelihood of an analog signal being exactlyequal to a digital value is small. Therefore, the analog to digitalconversion circuitry outputs a digital value either slightly higher orlower than the analog value. This determines the resolution, or leastsignificant bit, of the conversion of acceleration, a continuousphysical phenomenon, into a digital binary value. It is possible todevelop a more accurate estimate of the actual value of a point on ananalog waveform and achieve greater levels of resolution with theaddition of anti-alias filtering, dithering, oversampling, filteringquantization noise, and decimating the filtered, over-sampled signal.This can improve the least significant bit of the analog to digitalconversion process by several bits.

The two accelerometers 4702, 4704 are positioned at each end of thelongitudinal axis of an example motion and orientation sensing module ordevice. The forward tri-axial accelerometer 4704 tracks the movement ofthe leading edge, or active face, of the example instrument. Thisaccelerometer 4704 also tracks the orientation of the cross section ofthe example motion and orientation sensing module or device. Thetrailing accelerometer 4702 tracks the orientation of the longitudinalaxis of the motion and orientation module or device. The combination ofthe two tri-axial accelerometers 4702, 4704 can be used to measureheading and yaw in the X-Y plane with high accuracy and assure themotion and orientation sensing module or device can be guided preciselyto the target location and orientation in all three Cartesian axes withno discrepancies in pitch, roll, or yaw.

Motion and orientation sensing modules and devices having twoaccelerometers are not only capable of providing more accurate yaw data,but also two accelerometers provide a level of redundancy that aids inthe confirmation that the example instrument is guided accurately to thetarget position and orientation. If this cannot be achieved to therequired level of precision for both accelerometers the trackingprocedure may have been compromised and the user can be alerted to thepossibility of an exception condition that needs to be addressed.

The accelerometer 4702, 4704 outputs are routed to multiplexor (MUX)4606 through anti-alias low-pass filter 4904. Low-pass anti-aliasingfilter 4904 eliminates frequencies above the Nyquist frequency.Harmonics, intermodulation products, and other high frequency artifactscan be removed before oversampling the analog waveform because they canintroduce nonrandom distortions into the oversampling of dithered analogwaveforms. The sigma-delta analog to digital converter 5040 over-samplesthe analog signals output by accelerometers 4702, 4704 and filteredthrough anti-alias low-pass filter 4904. Dithering 4908 is introducedinto the filtered analog waveform and the analog signal is over-sampledby sigma-delta analog to digital converter 5040. The combination ofdithering 4908 and oversampling by the sigma-delta analog to digitalconverter 5040 enables the interpolation of analog values at each pointon the analog waveform. The digital values output by sigma-delta analogto digital conversion circuitry 5040 are filtered through quantizationfilter 4910 and input to decimator 4912. Filtering with quantizationnoise filter 4910 and down-sampling the over-sampled digital values withdecimator 4912 increases the signal-to-noise ratio of the analog todigital conversion process. Decimator 4912 digitally down-samples thestream of over-sampled digital values, and in conjunction with dithering4908 and oversampling 5040, can extend the effective number of bits byseveral least significant bits. The output of decimator 4912 drives datapacketizer 5034. Data packetizer 5034 assembles data into theappropriately formatted packets for transmission by telemetrytransceiver or transmitter 4122. The telemetry broadcasts are radiatedby antenna 4120. This enables an external computer system or otherinformation technology appliance to receive the radio frequency signalbroadcast by the motion and orientation sensing module or device forsubsequent processing, storage, and display in real time.

High-pass filter 4114 outputs high frequency signals form accelerometers4702, 4704 to event detection circuitry 5160. These signals are alsoinput to data packetizer 5034 for inclusion in the telemetry packets. Inaddition to high-pass filter 4114, event detection circuitry 5160 alsohas inputs from low-pass filter 4904 and directly from the accelerationsensing elements of accelerometers 4702, 4704, the voltage on battery4132, and readings from temperature sensor 5048. With this combinationof inputs it is possible to detect a wide range of potential exceptionconditions that could compromise the integrity of the tracking procedureand data. The analysis of event detection circuitry 5160 is transmittedto the computer to alert the user.

Data from temperature sensor 5048 are also incorporated into theautomatic calibration routine executed whenever a motion and orientationsensing module or device is powered up. The data gathered during theautomatic calibration routine are stored in nonvolatile memory 4136within the motion and orientation sensing module or device.

Control logic and calibration circuitry 5146 controls the operation ofthe electronic components within the motion and orientation sensingmodule or device as well as additional data processing that may berequired before transmitting the data to a computer system. Battery4132, or equivalent energy storage device, provides the power to operatethe electronic circuitry within the motion and orientation sensingmodule or device. Ratiometric design reduces sensitivity of the datacapture and conversion circuitry to fluctuations in supply and referencevoltages as well as noise on power conductors. Precision voltagereference 5050 provides additional protection against variations inreference voltages. Substrate 5120 provides mechanical support andelectrical interconnect for the electronic components and battery withinthe motion and orientation sensing module or device. The illustratedcomponents and interconnect will enable tracking the movement andorientation of a medical probe, tool, instrument, alignment jig, cuttingblock, or similar equipment having a motion and orientation sensingmodule or device, accurately with a high level of precision.

While the present invention has been described with reference toparticular embodiments, those skilled in the art will recognize thatmany changes may be made thereto without departing from the spirit andscope of the present invention. Each of these embodiments and obviousvariations thereof is contemplated as falling within the spirit andscope of the claimed invention, which is set forth in the claims. Whilethe subject matter of the invention is described with specific examplesof embodiments, the foregoing drawings and descriptions thereof depictonly typical embodiments of the subject matter and are not therefore tobe considered to be limiting of its scope, it is evident that manyalternatives and variations will be apparent to those skilled in theart. Thus, the description of the invention is merely descriptive innature and, thus, variations that do not depart from the gist of theinvention are intended to be within the scope of the embodiments of thepresent invention. Such variations are not to be regarded as a departurefrom the spirit and scope of the present invention.

While the present invention has been described with reference toembodiments, it is to be understood that the invention is not limited tothe disclosed embodiments. The scope of the following claims is to beaccorded the broadest interpretation so as to encompass allmodifications, equivalent structures and functions. For example, ifwords such as “orthogonal”, “perpendicular” are used the intendedmeaning is “substantially orthogonal” and “substantially perpendicular”respectively. Additionally although specific numbers may be quoted inthe claims, it is intended that a number close to the one stated is alsowithin the intended scope, i.e. any stated number (e.g., 90 degrees)should be interpreted to be “about” the value of the stated number(e.g., about 90 degrees).

As the claims hereinafter reflect, inventive aspects may lie in lessthan all features of a single foregoing disclosed embodiment. Thus, thehereinafter expressed claims are hereby expressly incorporated into thisDetailed Description of the Drawings, with each claim standing on itsown as a separate embodiment of an invention. Furthermore, while someembodiments described herein include some but not other featuresincluded in other embodiments, combinations of features of differentembodiments are meant to be within the scope of the invention, and formdifferent embodiments, as would be understood by those skilled in theart.

What is claimed is:
 1. An orthopedic position tracking systemcomprising: a first tri-axial accelerometer; a multiplexer (MUX) coupledto the first accelerometer; a capacitance to voltage converter coupledto the multiplexer; an analog to digital converter (ADC) coupled to thecapacitance to voltage converter; a transceiver coupled to the analog todigital converter configured to send position data from the system; andcontrol logic coupled to the first tri-axial accelerometer, themultiplexer, the ADC converter, and the transceiver configured tocontrol position measurement where the position tracking system isconfigured to sample at greater than 40 times per second allowingtracking within 1 millimeter over a path length less of 5 meters orless.
 2. The system of claim 1 further including a second tri-axialaccelerometer coupled to the multiplexer and the control logic where thefirst and second tri-axial accelerometers are respectively located atfirst and second positions and where the system is configured to trackorientation within 1 degree.
 3. The system of claim 2 where the analogto digital converter has a resolution of greater than 16 bits and wherethe position tracking system is configured to sample at greater than 100times per second.
 4. The system of claim 3 where the analog to digitalconverter has a resolution of at least 20 bits.
 5. The system of claim 3where a low-pass anti-aliasing filter is configured to filter a signalfrom the first or second tri-axial accelerometer.
 6. The system of claim4 where the system is configured to apply dithering to the signal fromthe first or second tri-axial accelerometer.
 7. The system of claim 5further including: a quantization noise filter coupled to the analog todigital converter where the analog to digital converter is anover-sampling analog to digital converter; and a decimator coupled tothe quantization noise filter.
 8. The system of claim 7 where the firstand second tri-axial accelerometers are capacitive accelerometers. 9.The system of claim 6 further including feedback circuitry configured tocounteract displacement of moveable capacitor plates.
 10. An orthopedicposition tracking system comprising: a first tri-axial capacitiveaccelerometer located in a first position; a second tri-axial capacitiveaccelerometer located in a second position; a multiplexer (MUX) coupledto the first and second accelerometers; a capacitance to voltageconverter coupled to the multiplexer; an analog to digital converter(ADC) coupled to the capacitance to voltage converter; a transceivercoupled to the analog to digital converter configured to send positiondata from the system; and control logic coupled to the firstaccelerometer, the second accelerometer, the multiplexer, the ADCconverter, and the transceiver configured to control positionmeasurement where the position tracking system samples at greater than40 times per second.
 11. The system of claim 10 where the analog todigital converter has a resolution of greater than 16 bits and where theposition tracking system is configured to track within 1 millimeter overa path length less of 5 meters or less and where the position trackingsystem is configured to provide orientation within 1 degree.
 12. Thesystem of claim 11 further including feedback circuitry configured tocounteract displacement of moveable capacitor plates.
 13. The system ofclaim 12 where a low-pass anti-aliasing filter is configured to filter asignal from the first or second tri-axial accelerometer and where thesystem is configured to apply dithering to the signal from the first orsecond tri-axial accelerometer.
 14. The system of claim 13 furtherincluding: a quantization noise filter coupled to the analog to digitalconverter where the analog to digital converter is an over-samplinganalog to digital converter; and a decimator coupled to the quantizationnoise filter.
 15. An orthopedic position tracking system comprising: afirst tri-axial piezo-resistive accelerometer located in a firstposition; a second tri-axial piezo-resistive accelerometer located in asecond position; a multiplexer (MUX) coupled to the first and secondtri-axial piezo-resistive accelerometers; an analog to digital converter(ADC) coupled to the multiplexer; a transceiver coupled to the analog todigital converter configured to send position data from the system; andcontrol logic coupled to the first tri-axial piezo-resistiveaccelerometer, the second tri-axial piezo-resistive accelerometer, themultiplexer, the ADC converter, and the transceiver configured tocontrol position measurement where the position tracking system isconfigured to sample at greater than 40 times per second, track within 1millimeter over a path length less of 5 meters or less, and to provideorientation within 1 degree.